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50 MCQs on Atoms and Molecules: Test Your Knowledge | The Govt Guide

50 MCQs on Atoms and Molecules: Test Your Knowledge | The Govt Guide

50 MCQs on Atoms and Molecules: Test Your Knowledge

By Rajesh Jaipal | The Govt Guide

Introduction to Atoms and Molecules MCQs

Atoms and molecules form the foundation of chemistry, governing the behavior of matter in the universe. Whether you're a student preparing for exams or a science enthusiast, these 50 multiple-choice questions (MCQs) on atoms and molecules will test your knowledge and deepen your understanding. Each question comes with the correct answer in dark green, along with a detailed explanation to clarify concepts like Dalton's atomic theory, chemical formulae, and molecular mass. Let’s dive in!

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MCQs on Atoms and Molecules

1. Who proposed the concept of Parmanu?

a) John Dalton

b) Antoine Lavoisier

c) Maharishi Kanad

d) Joseph Proust

Correct Answer: c) Maharishi Kanad

Explanation: Around 500 BC, Indian philosopher Maharishi Kanad proposed the idea of Parmanu, which he described as the smallest indivisible particle of matter, laying the foundation for atomic theory.

2. What did Democritus and Leucippus name the smallest indivisible particles?

a) Molecules

b) Atoms

c) Elements

d) Ions

Correct Answer: b) Atoms

Explanation: Greek philosophers Democritus and Leucippus, around 500 BC, named the smallest indivisible particles "atoms," meaning "indivisible" in Greek.

3. Who proposed the Law of Conservation of Mass?

a) John Dalton

b) Antoine Lavoisier

c) Joseph Proust

d) J.J. Berzelius

Correct Answer: b) Antoine Lavoisier

Explanation: Antoine Lavoisier, in the 18th century, proposed the Law of Conservation of Mass, stating that mass is neither created nor destroyed in a chemical reaction.

4. What does the Law of Definite Proportions state?

a) Mass is conserved in reactions

b) A chemical compound contains elements in fixed proportions

c) Atoms are indivisible

d) Elements combine in whole-number ratios

Correct Answer: b) A chemical compound contains elements in fixed proportions

Explanation: The Law of Definite Proportions, proposed by Joseph Proust, states that a chemical compound always contains the same elements in fixed proportions by mass, regardless of its source.

5. Who stated the Law of Definite Proportions?

a) Antoine Lavoisier

b) John Dalton

c) Joseph Proust

d) Maharishi Kanad

Correct Answer: c) Joseph Proust

Explanation: Joseph Proust, a French chemist, stated the Law of Definite Proportions in the late 18th century, providing evidence through experiments with compounds like water and ammonia.

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

a) 1:2

b) 1:8

c) 2:1

d) 8:1

Correct Answer: b) 1:8

Explanation: In water (H₂O), the mass ratio of hydrogen to oxygen is always 1:8, as determined by the Law of Definite Proportions.

7. What is the mass ratio of nitrogen to hydrogen in ammonia?

a) 14:3

b) 3:14

c) 1:3

d) 3:1

Correct Answer: a) 14:3

Explanation: In ammonia (NH₃), the mass ratio of nitrogen to hydrogen is 14:3, reflecting the fixed proportions of the elements in the compound.

8. Who proposed the atomic theory in 1808?

a) Antoine Lavoisier

b) John Dalton

c) Joseph Proust

d) J.J. Berzelius

Correct Answer: b) John Dalton

Explanation: John Dalton proposed his atomic theory in 1808, providing a scientific framework for the behavior of atoms in chemical reactions.

9. According to Dalton, atoms of a given element are:

a) Different in mass

b) Identical in mass and properties

c) Always divisible

d) Unstable

Correct Answer: b) Identical in mass and properties

Explanation: Dalton’s atomic theory states that atoms of a given element are identical in mass and chemical properties, distinguishing them from atoms of other elements.

10. What is the radius of a hydrogen atom?

a) 10⁻⁸ m

b) 10⁻⁹ m

c) 10⁻¹⁰ m

d) 10⁻¹¹ m

Correct Answer: c) 10⁻¹⁰ m

Explanation: The radius of a hydrogen atom is approximately 10⁻¹⁰ m, making it incredibly small and invisible to the naked eye.

11. What is the size of a water molecule?

a) 10⁻⁸ m

b) 10⁻⁹ m

c) 10⁻¹⁰ m

d) 10⁻¹¹ m

Correct Answer: b) 10⁻⁹ m

Explanation: A water molecule (H₂O) has a size of about 10⁻⁹ m, slightly larger than a single hydrogen atom due to its molecular structure.

12. What unit is used to measure atomic mass?

a) Gram

b) Kilogram

c) Atomic mass unit (u)

d) Mole

Correct Answer: c) Atomic mass unit (u)

Explanation: The atomic mass unit (u) is defined as 1/12th the mass of a carbon-12 atom and is used to measure the mass of atoms and molecules.

13. What is the atomic mass of carbon-12?

a) 1 u

b) 12 u

c) 16 u

d) 35.5 u

Correct Answer: b) 12 u

Explanation: Carbon-12 is the standard for atomic mass, with its mass defined as exactly 12 u, serving as a reference for other elements.

14. What is the atomic mass of hydrogen?

a) 1 u

b) 12 u

c) 16 u

d) 35.5 u

Correct Answer: a) 1 u

Explanation: The atomic mass of hydrogen is approximately 1 u, based on the carbon-12 standard.

15. What is the atomic mass of oxygen?

a) 1 u

b) 12 u

c) 16 u

d) 35.5 u

Correct Answer: c) 16 u

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

16. Who suggested symbols for elements using one or two letters?

a) John Dalton

b) J.J. Berzelius

c) Antoine Lavoisier

d) Joseph Proust

Correct Answer: b) J.J. Berzelius

Explanation: J.J. Berzelius simplified element notation by using one or two letters from the element’s name, a system later standardized by IUPAC.

17. What is the symbol for iron derived from?

a) Latin name Ferrum

b) Latin name Natrium

c) English name Iron

d) Greek name

Correct Answer: a) Latin name Ferrum

Explanation: The symbol for iron, Fe, is derived from its Latin name "Ferrum," following historical naming conventions.

18. What is the valency of magnesium?

a) 1

b) 2

c) 3

d) 4

Correct Answer: b) 2

Explanation: Magnesium has a valency of 2, meaning it can form two bonds, as seen in compounds like magnesium chloride (MgCl₂).

19. What is the valency of chlorine?

a) 1

b) 2

c) 3

d) 4

Correct Answer: a) 1

Explanation: Chlorine has a valency of 1, meaning it forms one bond, as seen in compounds like magnesium chloride (MgCl₂).

20. What is the chemical formula for magnesium chloride?

a) MgCl

b) MgCl₂

c) Mg₂Cl

d) MgCl₃

Correct Answer: b) MgCl₂

Explanation: Magnesium chloride is formed by criss-crossing the valencies of Mg²⁺ (valency 2) and Cl⁻ (valency 1), resulting in MgCl₂.

21. What is the valency of aluminium?

a) 1

b) 2

c) 3

d) 4

Correct Answer: c) 3

Explanation: Aluminium has a valency of 3, meaning it can form three bonds, as seen in compounds like aluminium oxide (Al₂O₃).

22. What is the chemical formula for aluminium oxide?

a) AlO

b) Al₂O₃

c) Al₃O₂

d) AlO₂

Correct Answer: b) Al₂O₃

Explanation: Aluminium oxide is formed by criss-crossing the valencies of Al³⁺ (valency 3) and O²⁻ (valency 2), resulting in Al₂O₃.

23. What is a polyatomic ion?

a) A single charged atom

b) A group of atoms with a net charge

c) A neutral molecule

d) A single element

Correct Answer: b) A group of atoms with a net charge

Explanation: A polyatomic ion is a group of atoms that carries a net charge, such as ammonium (NH₄⁺) or sulphate (SO₄²⁻).

24. What is the formula for ammonium sulphate?

a) NH₄SO₄

b) (NH₄)₂SO₄

c) NH₄(SO₄)₂

d) (NH₄)SO₄

Correct Answer: b) (NH₄)₂SO₄

Explanation: Ammonium sulphate is formed by combining two ammonium ions (NH₄⁺, valency 1) with one sulphate ion (SO₄²⁻, valency 2), resulting in (NH₄)₂SO₄.

25. What is the molecular mass of water (H₂O)?

a) 16 u

b) 18 u

c) 20 u

d) 22 u

Correct Answer: b) 18 u

Explanation: The molecular mass of water (H₂O) is calculated as 2 × 1 u (hydrogen) + 16 u (oxygen) = 18 u.

26. What is the molecular mass of nitric acid (HNO₃)?

a) 53 u

b) 63 u

c) 73 u

d) 83 u

Correct Answer: b) 63 u

Explanation: The molecular mass of nitric acid (HNO₃) is 1 u (H) + 14 u (N) + 3 × 16 u (O) = 1 + 14 + 48 = 63 u.

27. What is the formula unit mass of sodium chloride (NaCl)?

a) 48.5 u

b) 58.5 u

c) 68.5 u

d) 78.5 u

Correct Answer: b) 58.5 u

Explanation: The formula unit mass of sodium chloride (NaCl) is 23 u (Na) + 35.5 u (Cl) = 58.5 u.

28. What is the formula unit mass of calcium chloride (CaCl₂)?

a) 91 u

b) 101 u

c) 111 u

d) 121 u

Correct Answer: c) 111 u

Explanation: The formula unit mass of calcium chloride (CaCl₂) is 40 u (Ca) + 2 × 35.5 u (Cl) = 40 + 71 = 111 u.

29. What is an element?

a) A mixture of compounds

b) A pure substance made of one type of atom

c) A charged particle

d) A group of molecules

Correct Answer: b) A pure substance made of one type of atom

Explanation: An element is a pure substance made of atoms with the same number of protons, such as hydrogen (H) or oxygen (O).

30. What is a compound?

a) A single atom

b) A substance formed by two or more elements

c) A charged particle

d) A mixture of elements

Correct Answer: b) A substance formed by two or more elements

Explanation: A compound is a substance formed by the chemical combination of two or more elements in fixed proportions, like water (H₂O).

31. What type of molecule is oxygen (O₂)?

a) Monoatomic

b) Diatomic

c) Triatomic

d) Tetratomic

Correct Answer: b) Diatomic

Explanation: Oxygen (O₂) is a diatomic molecule, meaning it consists of two atoms of oxygen bonded together.

32. How many atoms are in a water molecule (H₂O)?

a) 1

b) 2

c) 3

d) 4

Correct Answer: c) 3

Explanation: A water molecule (H₂O) contains 2 hydrogen atoms and 1 oxygen atom, totaling 3 atoms.

33. What is the charge of a sodium ion?

a) +1

b) -1

c) +2

d) -2

Correct Answer: a) +1

Explanation: A sodium ion (Na⁺) carries a charge of +1, as it loses one electron to achieve stability.

34. What is the charge of a chloride ion?

a) +1

b) -1

c) +2

d) -2

Correct Answer: b) -1

Explanation: A chloride ion (Cl⁻) carries a charge of -1, as it gains one electron to achieve stability.

35. What is the charge of an ammonium ion?

a) +1

b) -1

c) +2

d) -2

Correct Answer: a) +1

Explanation: An ammonium ion (NH₄⁺) is a polyatomic ion with a charge of +1, commonly found in compounds like ammonium sulphate.

36. What is the charge of a sulphate ion?

a) +1

b) -1

c) +2

d) -2

Correct Answer: d) -2

Explanation: A sulphate ion (SO₄²⁻) is a polyatomic ion with a charge of -2, often seen in compounds like ammonium sulphate.

37. What does IUPAC standardize?

a) Chemical reactions

b) Element names and symbols

c) Atomic sizes

d) Molecular masses

Correct Answer: b) Element names and symbols

Explanation: IUPAC (International Union of Pure and Applied Chemistry) standardizes element names, symbols, and units to ensure global consistency in chemistry.

38. What is the valency of hydrogen?

a) 1

b) 2

c) 3

d) 4

Correct Answer: a) 1

Explanation: Hydrogen has a valency of 1, meaning it can form one bond, as seen in compounds like hydrogen chloride (HCl).

39. What is the valency of oxygen?

a) 1

b) 2

c) 3

d) 4

Correct Answer: b) 2

Explanation: Oxygen has a valency of 2, meaning it can form two bonds, as seen in compounds like water (H₂O).

40. What is the chemical formula for hydrogen chloride?

a) HCl

b) H₂Cl

c) HCl₂

d) H₂Cl₂

Correct Answer: a) HCl

Explanation: Hydrogen chloride is formed by combining one hydrogen atom (valency 1) and one chlorine atom (valency 1), resulting in HCl.

41. What is the symbol for sodium derived from?

a) Latin name Natrium

b) Latin name Ferrum

c) English name Sodium

d) Greek name

Correct Answer: a) Latin name Natrium

Explanation: The symbol for sodium, Na, is derived from its Latin name "Natrium," a historical naming convention.

42. What is the atomic mass of chlorine?

a) 16 u

b) 23 u

c) 35.5 u

d) 40 u

Correct Answer: c) 35.5 u

Explanation: The atomic mass of chlorine is approximately 35.5 u, based on the carbon-12 standard.

43. What is the atomic mass of calcium?

a) 16 u

b) 23 u

c) 35.5 u

d) 40 u

Correct Answer: d) 40 u

Explanation: The atomic mass of calcium is approximately 40 u, based on the carbon-12 standard.

44. What is the molecular mass of hydrogen sulphide (H₂S)?

a) 34 u

b) 36 u

c) 38 u

d) 40 u

Correct Answer: a) 34 u

Explanation: The molecular mass of hydrogen sulphide (H₂S) is 2 × 1 u (H) + 32 u (S) = 2 + 32 = 34 u.

45. What type of molecule is phosphorus (P₄)?

a) Monoatomic

b) Diatomic

c) Triatomic

d) Tetratomic

Correct Answer: d) Tetratomic

Explanation: Phosphorus (P₄) is a tetratomic molecule, meaning it consists of four phosphorus atoms bonded together.

46. What is the size of a haemoglobin molecule?

a) 10⁻⁸ m

b) 10⁻⁹ m

c) 10⁻¹⁰ m

d) 10⁻¹¹ m

Correct Answer: a) 10⁻⁸ m

Explanation: A haemoglobin molecule has a size of about 10⁻⁸ m, larger than a water molecule due to its complex structure.

47. What is the mass ratio of carbon to oxygen in carbon dioxide?

a) 1:2

b) 2:1

c) 3:8

d) 8:3

Correct Answer: c) 3:8

Explanation: In carbon dioxide (CO₂), the mass ratio of carbon to oxygen is 3:8, as determined by the Law of Definite Proportions.

48. Can atoms exist independently?

a) Yes, always

b) No, except for noble gases

c) No, never

d) Yes, but only in compounds

Correct Answer: b) No, except for noble gases

Explanation: Most atoms cannot exist independently and form molecules or ions to achieve stability, except for noble gases like argon and helium.

49. What is the primary source of atomic mass standards?

a) Hydrogen-1

b) Oxygen-16

c) Carbon-12

d) Chlorine-35

Correct Answer: c) Carbon-12

Explanation: Carbon-12 is the primary standard for atomic mass, with its mass defined as exactly 12 u, used to measure the mass of other elements.

50. What law supports the idea that mass is conserved in reactions?

a) Law of Definite Proportions

b) Law of Conservation of Mass

c) Dalton’s Atomic Theory

d) Law of Multiple Proportions

Correct Answer: b) Law of Conservation of Mass

Explanation: The Law of Conservation of Mass, proposed by Antoine Lavoisier, states that mass is neither created nor destroyed in a chemical reaction, supporting the idea of mass conservation.

Conclusion

These 50 MCQs on atoms and molecules provide a comprehensive way to test and enhance your understanding of fundamental chemistry concepts. From the historical insights of atomic theory to practical applications like calculating molecular mass, this quiz covers it all. Keep practicing and exploring with The Govt Guide to master chemistry!

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My name is Rajesh Kumar, and I am from Gharsana, Sri Ganganagar in Rajasthan. I have completed my Bachelor of Science (B.Sc.) in 2017 and Bachelor of Education (B.Ed.) in 2019 from Maharaja Ganga Singh University, Bikaner. I hold a Master’s degree (M.A.) in Philosophy, completed in 2022, and I am currently pursuing M.A. in Sociology. I have work experience in the insurance sector and possess strong skills in MS Office, typing, and I hold a certificate in RSCIT. I am fluent in Hindi, Punjabi, and English. At present, I am preparing for competitive exams like DSSSB and UGC NET (Philosophy). I also run educational blog called “The Govt Guide” & "Literary Sphere", where I post content related to NCERT Notes, Govt job vacancy, literature and exam preparation. My hobbies include playing chess and reading books.