Which of the following is a polyatomic ion?

Correct Option: C. Solution: NH₄⁺ is a polyatomic ion known as ammonium.

Which of the following elements has an atomic mass of 14 u?

Correct Option: C. Solution: Nitrogen has an atomic mass of 14 u.

Atoms and Molecules

Objectives Notes Exam Tips Practice Qs Ask AI

Learning Objectives

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Understand and apply the Law of Conservation of Mass in chemical reactions.
Calculate the percentage composition of compounds based on mass.
Identify and write chemical formulae for various compounds.
Determine the molar mass of given substances.
Explain the concept of polyatomic ions and provide examples.
Recognize and apply the laws of chemical combination in practical scenarios.

Revision Notes & Summary

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Chapter 3: Atoms and Molecules

3.1 Laws of Chemical Combination

3.1.1 Law of Conservation of Mass

During a chemical reaction, the sum of the masses of the reactants and products remains unchanged.

3.1.2 Law of Definite Proportions

In a pure chemical compound, elements are always present in a definite proportion by mass.

3.2 What is an Atom?

Atoms are the smallest particles of an element that cannot usually exist independently and retain all their chemical properties.
Dalton's atomic theory proposed that each element has a characteristic atomic mass.

3.2.1 Modern Symbols of Atoms of Different Elements

Symbols are derived from the first one or two letters of the element's name.

Element	Symbol	Element	Symbol	Element	Symbol
Aluminium	Al	Copper	Cu	Nitrogen	N
Argon	Ar	Fluorine	F	Oxygen	O
Barium	Ba	Gold	Au	Potassium	K
Boron	B	Hydrogen	H	Silicon	Si
Bromine	Br	Iodine	I	Silver	Ag
Calcium	Ca	Iron	Fe	Sodium	Na
Carbon	C	Lead	Pb	Sulphur	S
Chlorine	Cl	Magnesium	Mg	Uranium	U
Cobalt	Co	Neon	Ne	Zinc	Zn

3.2.2 Atomic Mass

The atomic mass unit (u) is defined as equal to the mass of one carbon atom.

3.3 Molecules of Elements and Compounds

3.3.1 Molecules of Elements

Molecules of an element consist of the same type of atoms.
Example: Oxygen (O₂) is a diatomic molecule.

3.3.2 Molecules of Compounds

Atoms of different elements join together in definite proportions to form molecules of compounds.

Compound	Combining Elements	Ratio by Mass
Water (H₂O)	Hydrogen, Oxygen	1:8
Ammonia (NH₃)	Nitrogen, Hydrogen	14:3
Carbon Dioxide (CO₂)	Carbon, Oxygen	3:8

3.3.3 What is an Ion?

Ions are charged species that can consist of a single charged atom or a group of atoms with a net charge.
A negatively charged ion is called an anion, while a positively charged ion is called a cation.

Exercises

Calculate the percentage composition of a compound of oxygen and boron.
Determine the mass of carbon dioxide produced from burning carbon in oxygen.
Define polyatomic ions and provide examples.
Write chemical formulae for specified compounds.
Calculate the molar mass of various substances.

Exam Tips & Common Mistakes

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Common Mistakes and Exam Tips

Common Pitfalls

Misunderstanding Chemical Formulas: Students often confuse the symbols and valencies of elements when writing chemical formulas. Ensure you understand the correct valency of each element.
Ignoring Mass Ratios: When calculating the mass of reactants and products, students sometimes forget to apply the law of conservation of mass, leading to incorrect conclusions about mass changes in reactions.
Confusing Atoms and Molecules: Students may confuse the definitions of atoms and molecules. Remember, an atom is the smallest unit of an element, while a molecule is a group of two or more atoms bonded together.
Incorrect Calculation of Molar Mass: Errors often occur in calculating the molar mass of compounds. Double-check your atomic masses and ensure you account for the number of each type of atom in the formula.

Tips for Success

Practice Writing Formulas: Engage in activities that involve writing chemical formulas using symbols and valencies. This will help reinforce your understanding.
Use Tables for Atomic Masses: Familiarize yourself with tables of atomic masses and symbols for elements to avoid confusion during calculations.
Understand Laws of Chemical Combination: Make sure you can explain and apply the law of conservation of mass and the law of definite proportions in your answers.
Review Polyatomic Ions: Be clear on what polyatomic ions are and be able to identify examples, as they often appear in chemical reactions and formulas.

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Practice Test – MCQs, True/False

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Multiple Choice Questions

Hydrogen

Iron

Sodium

Potassium

Correct Answer: A

Solution:

The symbol for hydrogen is H, which is derived from its English name.

5:2

3:4

23:35.5

1:1

Correct Answer: A

Solution:

The mass ratio of calcium to oxygen in calcium oxide is 5:2.

Na⁺

Cl⁻

NH₄⁺

O²⁻

Correct Answer: C

Solution:

NH₄⁺ is a polyatomic ion known as ammonium.

11 g

14 g

50 g

53 g

Correct Answer: A

Solution:

According to the law of conservation of mass, 3 g of carbon and 8 g of oxygen produce 11 g of carbon dioxide. Excess oxygen does not change the amount of carbon dioxide formed.

54 g

44 g

48 g

56 g

Correct Answer: D

Solution:

According to the Law of Conservation of Mass, the total mass of reactants equals the total mass of products. Therefore, the mass of water formed is

6 \text{ g (H)} + 48 \text{ g (O)} = 54 \text{ g (H}_2\text{O)}

A single atom of hydrogen

A group of two or more atoms chemically bonded together

A single electron

A mixture of different elements

Correct Answer: B

Solution:

A molecule is a group of two or more atoms that are chemically bonded together.

Correct Answer: A

Solution:

Sodium has a valency of 1, as it forms Na⁺ ions in sodium chloride.

40%

50%

60%

70%

Correct Answer: C

Solution:

The mass of oxygen in the compound is 0.24 g - 0.096 g = 0.144 g. The percentage by weight of oxygen is (0.144 g / 0.24 g) * 100% = 60%.

27 g

24 g

21 g

3 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the total mass of reactants equals the total mass of products. Thus, 3 g of hydrogen and 24 g of oxygen produce 27 g of water.

u (unified mass)

g (gram)

kg (kilogram)

mol (mole)

Correct Answer: A

Solution:

The atomic mass unit is now referred to as 'u' (unified mass) according to the latest IUPAC recommendations.

The mass of the reactants is equal to the mass of the products in a chemical reaction.

The mass of the reactants is always greater than the mass of the products.

The mass of the reactants is always less than the mass of the products.

Mass is not conserved in a chemical reaction.

Correct Answer: A

Solution:

According to the Law of Conservation of Mass, the mass of the reactants is equal to the mass of the products in a chemical reaction.

Mass is created

Mass is destroyed

Mass remains unchanged

Mass is converted to energy

Correct Answer: C

Solution:

The Law of Conservation of Mass states that the total mass of reactants and products remains unchanged during a chemical reaction.

1:2

1:1

2:1

3:2

Correct Answer: B

Solution:

The mass ratio is calculated by dividing the mass of magnesium by the mass of oxygen. Thus, the ratio is

\frac{2}{4} = \frac{1}{2}

, which simplifies to 1:1.

128 u

256 u

64 u

32 u

Correct Answer: B

Solution:

The molar mass of a sulphur molecule S₈ is 8 times the atomic mass of sulphur: 8 * 32 u = 256 u.

18 g

27 g

24 g

21 g

Correct Answer: B

Solution:

According to the law of conservation of mass, the total mass of reactants equals the total mass of products. Therefore, 3 g of hydrogen + 24 g of oxygen = 27 g of water produced.

Sodium

Aluminium

Chlorine

Zinc

Correct Answer: A

Solution:

The symbol for sodium is 'Na', derived from its Latin name 'natrium'.

NaCl

H₂O

Correct Answer: B

Solution:

H₂O is a molecule consisting of two hydrogen atoms and one oxygen atom bonded together.

Sodium

Oxygen

Chlorine

Carbon

Correct Answer: A

Solution:

The symbol for sodium is Na, derived from its Latin name 'natrium'.

24 g/mol

26 g/mol

28 g/mol

30 g/mol

Correct Answer: C

Solution:

The molar mass of ethyne (C₂H₂) is calculated as follows: (2 × 12 u for carbon) + (2 × 1 u for hydrogen) = 24 u + 2 u = 26 u, which is 26 g/mol.

The atomic mass of the element

The number of protons in the element

The combining power of an element

The number of electrons in the element

Correct Answer: C

Solution:

The valency of an element is its combining power, which determines how it combines with other elements.

60%

40%

50%

70%

Correct Answer: A

Solution:

The mass of oxygen in the compound is 0.24 g - 0.096 g = 0.144 g. The percentage of oxygen is (0.144 g / 0.24 g) * 100% = 60%.

The mass of a single atom of the element.

The average mass of the atoms of the element compared to 1/12th the mass of a carbon-12 atom.

The mass of an electron in the element.

The mass of a proton in the element.

Correct Answer: B

Solution:

The atomic mass of an element is the average mass of its atoms compared to 1/12th the mass of a carbon-12 atom.

26 g

16 g

10 g

6 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the total mass of reactants equals the total mass of products. Therefore, the mass of calcium oxide formed is 10 g + 16 g = 26 g.

Law of Definite Proportions

Law of Multiple Proportions

Law of Conservation of Mass

Law of Constant Composition

Correct Answer: C

Solution:

The Law of Conservation of Mass states that the mass of reactants equals the mass of products in a chemical reaction.

6 g

3 g

8 g

5 g

Correct Answer: A

Solution:

The proportion of X to Y in the compound is 2:3. If 4 g of X is used, maintaining the same proportion, we need 6 g of Y (since 4/2 = 2, and 2 * 3 = 6).

1:2

1:8

2:1

8:1

Correct Answer: B

Solution:

Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water.

NH₄⁺

Cl⁻

SO₄²⁻

CO₃²⁻

Correct Answer: B

Solution:

Cl⁻ is a monatomic ion, not a polyatomic ion. Polyatomic ions consist of multiple atoms, such as NH₄⁺, SO₄²⁻, and CO₃²⁻.

35 g

40 g

45 g

50 g

Correct Answer: A

Solution:

The mass of compound MN formed is the mass of M that reacted (10 g - 5 g = 5 g) plus the mass of N (30 g). Therefore, the mass of compound MN is 5 g + 30 g = 35 g.

11 g

53 g

8 g

3 g

Correct Answer: A

Solution:

According to the law of definite proportions, 3 g of carbon reacts with 8 g of oxygen to produce 11 g of carbon dioxide. Excess oxygen does not affect the amount of carbon dioxide produced.

Atomic mass is the mass of an electron.

Atomic mass is the mass of a proton.

Atomic mass is the mass of an atom relative to 1/12th the mass of a carbon-12 atom.

Atomic mass is the mass of a neutron.

Correct Answer: C

Solution:

Dalton's atomic theory led to the concept of atomic mass, which is defined as the mass of an atom relative to 1/12th the mass of a carbon-12 atom.

25 g

20 g

15 g

5 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the mass of reactants must equal the mass of the products. Therefore, the total mass of compound XY₂ formed is 5 g + 20 g = 25 g.

Law of Definite Proportions

Law of Conservation of Mass

Law of Multiple Proportions

Law of Constant Composition

Correct Answer: B

Solution:

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction.

A single atom

A group of atoms bonded together

An ion with a positive charge

An element in its pure form

Correct Answer: B

Solution:

A molecule is a group of two or more atoms that are chemically bonded together.

36 g

32 g

8 g

4 g

Correct Answer: A

Solution:

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the reactants (4 g of hydrogen + 32 g of oxygen = 36 g) will equal the total mass of the products, which is 36 g of water.

Law of Conservation of Mass

Law of Definite Proportions

Law of Multiple Proportions

Law of Constant Composition

Correct Answer: B

Solution:

The Law of Definite Proportions states that in a pure chemical compound, elements are always present in a definite proportion by mass.

23 g

16 g

7 g

14 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the total mass of the reactants equals the total mass of the products. Therefore, the mass of nitrogen dioxide formed is 7 g + 16 g = 23 g.

28 u

32 u

44 u

48 u

Correct Answer: C

Solution:

The molecular mass of CO₂ is calculated as: Carbon (12 u) + 2 × Oxygen (16 u) = 44 u.

5:2

2:5

1:1

3:2

Correct Answer: A

Solution:

The mass ratio of calcium to oxygen in calcium oxide is 5:2, as given by the masses of the reactants that completely react to form the compound.

3 g

5 g

7 g

10 g

Correct Answer: A

Solution:

According to the Law of Conservation of Mass, the total mass of reactants must equal the total mass of products. Therefore, the mass of substance D is calculated as follows:

5 \text{ g (A)} + 10 \text{ g (B)} = 12 \text{ g (C)} + x \text{ g (D)}

. Solving for

x

, we get

x = 3 \text{ g}

Hydrogen

Carbon

Oxygen

Nitrogen

Correct Answer: B

Solution:

Carbon has an atomic mass of 12 u as per the atomic mass table.

A₂B

AB₂

A₂B₃

Correct Answer: B

Solution:

The simplest formula is determined by the mole ratio. Moles of A = 3 g / 6 u = 0.5 moles, Moles of B = 12 g / 24 u = 0.5 moles. The simplest ratio is 1:1, but since B is twice the atomic mass of A, the simplest formula is A₂B.

12 u

14 u

16 u

18 u

Correct Answer: C

Solution:

The atomic mass of oxygen is 16 u as per the standard atomic mass table.

12 u

14 u

16 u

18 u

Correct Answer: C

Solution:

The atomic mass of oxygen is 16 u, based on the carbon-12 standard.

The total mass of reactants is equal to the total mass of products in a chemical reaction.

Mass can be created or destroyed in a chemical reaction.

The mass of a compound is always greater than the sum of the masses of its elements.

Mass is irrelevant in chemical reactions.

Correct Answer: A

Solution:

The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products. This principle was established by Antoine L. Lavoisier.

It is based on the mass of one hydrogen atom.

It is equal to the mass of one oxygen atom.

It is defined as one-twelfth the mass of a carbon-12 atom.

It is equivalent to the mass of one nitrogen atom.

Correct Answer: C

Solution:

The atomic mass unit (amu) is defined as one-twelfth the mass of a carbon-12 atom, which is a standard reference for measuring atomic masses.

72 g

56 g

64 g

8 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the mass of the reactants equals the mass of the products. Thus, the mass of water produced is 8 g + 64 g = 72 g.

28 u

44 u

32 u

40 u

Correct Answer: B

Solution:

The molecular mass of carbon dioxide is calculated by adding the atomic masses of one carbon atom and two oxygen atoms:

12 \text{ u (C)} + 2 \times 16 \text{ u (O)} = 44 \text{ u}

1/12th the mass of a carbon-12 atom

1/16th the mass of an oxygen atom

1/14th the mass of a nitrogen atom

1/23rd the mass of a sodium atom

Correct Answer: A

Solution:

The atomic mass unit is defined as 1/12th the mass of a carbon-12 atom, according to IUPAC standards.

18 g

36 g

54 g

72 g

Correct Answer: B

Solution:

The reaction is 2H₂ + O₂ → 2H₂O. The molar mass of water (H₂O) is 18 g/mol. Since 2 moles of water are produced, the total mass is 2 × 18 g = 36 g.

Hydrogen

Carbon

Nitrogen

Oxygen

Correct Answer: C

Solution:

Nitrogen has an atomic mass of 14 u.

Oxygen

Sulphur

Phosphorus

Calcium

Correct Answer: A

Solution:

Oxygen (O₂) is a diatomic molecule, meaning it consists of two atoms.

Carbon-12 is abundant and forms compounds with many elements.

Carbon-12 is the heaviest element.

Carbon-12 is the lightest element.

Carbon-12 is the only isotope of carbon.

Correct Answer: A

Solution:

The atomic mass unit is based on carbon-12 because it is abundant, stable, and forms compounds with many elements, making it a convenient standard for measuring atomic masses.

A single atom with a positive charge

A group of atoms carrying a charge

A molecule with no charge

A single atom with a negative charge

Correct Answer: B

Solution:

A polyatomic ion is a group of atoms that are covalently bonded together and carry an overall charge, either positive or negative.

Iron

Copper

Gold

Silver

Correct Answer: A

Solution:

The symbol for iron is 'Fe', which is derived from its Latin name 'ferrum'.

12 u

16 u

24 u

32 u

Correct Answer: C

Solution:

The atomic mass of magnesium is 24 u.

15 g

5 g

10 g

20 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the total mass of the reactants equals the total mass of the products. Therefore, the total mass of the products will be 5 g + 10 g = 15 g.

1/16th the mass of an oxygen atom

1/12th the mass of a carbon-12 atom

The mass of a hydrogen atom

The mass of a helium atom

Correct Answer: B

Solution:

The atomic mass unit is defined as 1/12th the mass of a carbon-12 atom.

Barium sulphate

Sodium chloride

Barium chloride

Sodium sulphate

Correct Answer: A

Solution:

When barium chloride (BaCl₂) is mixed with sodium sulphate (Na₂SO₄), barium sulphate (BaSO₄) is formed as a precipitate due to its low solubility in water.

Molecules are always made of one atom.

Molecules can consist of two or more atoms bonded together.

Molecules are the smallest particles of an element that can exist independently.

Molecules are always visible to the naked eye.

Correct Answer: B

Solution:

A molecule is generally a group of two or more atoms that are chemically bonded together.

11.00 g

14.00 g

53.00 g

61.00 g

Correct Answer: A

Solution:

According to the law of conservation of mass, the mass of reactants equals the mass of products. Thus, 3.0 g of carbon and 8.0 g of oxygen produce 11.0 g of carbon dioxide. Any excess oxygen does not affect the mass of carbon dioxide formed.

8 g

11 g

3 g

5 g

Correct Answer: B

Solution:

According to the given data, 3 g of carbon reacts with 8 g of oxygen to produce 11 g of carbon dioxide.

8 g

24 g

16 g

32 g

Correct Answer: A

Solution:

Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. Therefore, 3 g of hydrogen would require 24 g of oxygen.

Atoms are indivisible particles.

Atoms of the same element are identical in mass and properties.

Atoms combine in simple whole-number ratios to form compounds.

Atoms cannot be created or destroyed in a chemical reaction.

Correct Answer: C

Solution:

The law of definite proportions states that a chemical compound always contains its component elements in a fixed ratio by mass. Dalton's postulate that atoms combine in simple whole-number ratios to form compounds supports this law.

40%

50%

60%

70%

Correct Answer: A

Solution:

The total mass of the compound is 0.24 g. The percentage of boron is (0.096/0.24) * 100% = 40%.

True or False

Correct Answer: True

Solution:

Dalton's atomic theory introduced the concept of atomic mass, suggesting that each element has a characteristic atomic mass, which helped explain the law of constant proportions.

Correct Answer: True

Solution:

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, so the mass of the reactants equals the mass of the products.

Correct Answer: True

Solution:

Ancient Indian philosophers like Maharishi Kanad postulated that matter is made up of indivisible particles called 'Parmanu'.

Correct Answer: True

Solution:

IUPAC is an international scientific organization that approves names of elements, symbols, and units.

Correct Answer: True

Solution:

The symbol for sodium is 'Na', which is derived from its Latin name 'natrium'.

Correct Answer: False

Solution:

Democritus and Leucippus suggested that matter, when divided, would eventually reach an indivisible particle called an atom.

Correct Answer: True

Solution:

The symbol for sodium is 'Na', which is derived from its Latin name 'natrium'.

Correct Answer: True

Solution:

A chemical formula indicates the types and numbers of atoms in a molecule of a compound, reflecting the ratio of its constituent elements.

Correct Answer: False

Solution:

Atoms of most elements cannot exist independently; they form molecules or ions to achieve stability.

Correct Answer: True

Solution:

The Law of Conservation of Mass is a fundamental principle in chemistry that asserts the total mass in a closed system remains constant, regardless of the processes acting inside the system.

Correct Answer: False

Solution:

Atoms of most elements cannot exist independently; they form molecules and ions to exist in nature.

Correct Answer: True

Solution:

The atomic mass unit (amu) is defined as exactly one-twelfth the mass of a carbon-12 atom, providing a standard for measuring atomic masses.

Correct Answer: False

Solution:

Atoms of most elements do not exist independently; they form molecules or ions to achieve stability.

Correct Answer: True

Solution:

Initially, 1/16th of the mass of an atom of naturally occurring oxygen was used as the atomic mass unit.

Correct Answer: True

Solution:

Scientists initially used 1/16th of the mass of an oxygen atom as the atomic mass unit before switching to 1/12th of the mass of a carbon-12 atom.

Correct Answer: True

Solution:

The name 'copper' is derived from 'Cyprus', which is the place where it was first found. This is an example of how some elements were named based on their place of discovery.

Correct Answer: True

Solution:

The atomic mass of oxygen is indeed 16 atomic mass units (u), as listed in standard atomic mass tables.

Correct Answer: True

Solution:

A chemical formula represents the composition of a compound, indicating the elements present and the number of atoms of each element in the compound.

Correct Answer: True

Solution:

Democritus and Leucippus, ancient Greek philosophers, suggested that matter could be divided until reaching indivisible particles called atoms.

Correct Answer: False

Solution:

The atomic mass unit is defined as one-twelfth the mass of an atom of carbon-12, not carbon-14.

Correct Answer: False

Solution:

Dalton's atomic theory proposed that each element has a characteristic atomic mass, distinguishing it from atoms of other elements.

Atoms and Molecules

Learning Objectives

Revision Notes & Summary

Chapter 3: Atoms and Molecules

3.1 Laws of Chemical Combination

3.1.1 Law of Conservation of Mass

3.1.2 Law of Definite Proportions

3.2 What is an Atom?

3.2.1 Modern Symbols of Atoms of Different Elements

3.2.2 Atomic Mass

3.3 Molecules of Elements and Compounds

3.3.1 Molecules of Elements

3.3.2 Molecules of Compounds

3.3.3 What is an Ion?

Exercises

Exam Tips & Common Mistakes

Common Mistakes and Exam Tips

Common Pitfalls

Tips for Success

AI Learning Assistant

Practice Test – MCQs, True/False

Multiple Choice Questions

Q1.Which of the following elements has a symbol derived from its English name?

Correct Answer: A

Q2.If a compound is formed by the combination of calcium and oxygen, what is the ratio of their masses?

Correct Answer: A

Q3.Which of the following is a polyatomic ion?

Correct Answer: C

Q4.If 3 g of carbon is burnt in 8 g of oxygen to produce 11 g of carbon dioxide, how much carbon dioxide will be formed when 3 g of carbon is burnt in 50 g of oxygen?

Correct Answer: A

Q5.When 6 g of hydrogen reacts completely with 48 g of oxygen, how much water is formed?

Correct Answer: D

Q6.Which of the following is a correct representation of a molecule?

Correct Answer: B

Q7.What is the valency of sodium in sodium chloride?

Correct Answer: A

Q8.A 0.24 g sample of a compound of oxygen and boron was found to contain 0.096 g of boron. What is the percentage by weight of oxygen in the compound?

Correct Answer: C

Q9.If 3 g of hydrogen reacts with 24 g of oxygen, how much water is formed?

Correct Answer: A

Q10.What is the atomic mass unit (amu) now referred to as, according to the latest IUPAC recommendations?

Correct Answer: A

Q11.Which of the following statements is true according to the Law of Conservation of Mass?

Correct Answer: A

Q12.According to the Law of Conservation of Mass, what happens during a chemical reaction?

Correct Answer: C

Q13.If 2 g of magnesium reacts with 4 g of oxygen to form magnesium oxide, what is the mass ratio of magnesium to oxygen in magnesium oxide?

Correct Answer: B

Q14.What is the molar mass of sulphur molecule S₈? (Given atomic mass of sulphur = 32 u)

Correct Answer: B

Q15.If 3 g of hydrogen reacts with 24 g of oxygen to form water, what mass of water is produced?

Correct Answer: B

Q16.Which of the following elements has a symbol derived from its Latin name?

Correct Answer: A

Q17.Which of the following is a molecule?

Correct Answer: B

Q18.Which of the following elements has a symbol derived from its Latin name?

Correct Answer: A

Q19.What is the molar mass of ethyne (C₂H₂)? Given atomic masses: C = 12 u, H = 1 u.

Correct Answer: C

Q20.What is the valency of an element?

Correct Answer: C

Q21.A compound of boron and oxygen has a total mass of 0.24 g and contains 0.096 g of boron. What is the percentage of oxygen in the compound?

Correct Answer: A

Q22.The atomic mass of an element is defined as:

Correct Answer: B

Q23.In a chemical reaction, 10 g of calcium reacts with 16 g of oxygen to form calcium oxide. According to the law of conservation of mass, what is the total mass of calcium oxide formed?

Correct Answer: A

Q24.Which law states that the mass of reactants equals the mass of products in a chemical reaction?

Correct Answer: C

Q25.A compound is formed by 2 g of element X and 3 g of element Y. If another compound is formed with 4 g of element X, how much of element Y is required to maintain the same proportion by mass?

Correct Answer: A

Q26.What is the ratio of hydrogen to oxygen by mass in water?

Correct Answer: B

Q27.Which of the following is NOT a polyatomic ion?

Correct Answer: B

Q28.Consider a reaction where 10 g of substance M reacts with 30 g of substance N to form compound MN. If 5 g of M remains unreacted, what is the mass of compound MN formed?

Correct Answer: A

Q29.If 3 g of carbon reacts with 8 g of oxygen to form carbon dioxide, how much carbon dioxide will be produced when 3 g of carbon reacts with 50 g of oxygen?

Correct Answer: A