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Basic Concepts of Chemistry Online Mcqs Test

Maan AliLast Updated: October 14, 2025

Important Basic Concepts of Chemistry Question and Answer

Total Questions:	71
Time Allowed:	30 Minutes
Total Marks:	71
How to Attempt Test:	Please choose the right Option in MCQ-type question.
Test Helpful For:	Chemistry Test ECAT Test MDCAT Test FPSC/PPSC/SPSC/KPPSC/BPSC/AJKPSC/NTS Chemistry Interview Question Answer

Basic Concepts of Chemistry Practice Test Online With Explanation

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Page 1 of 3

1. Isotopes differ in the

Number of electrons

Number of protons

Number of neutrons

Number of atoms

2. The modern atomic weight scale is based on

H¹

C¹³

O¹⁶

C¹²

3. An oxide of nitrogen contain 36.8% nitrogen and 63.2% oxygen by mass. Calculate its empirical formula.

NO₂

N₂O₃

N₂O

4. Which of the following represents a compound?

A pure substance made up of one type of atom

Made up of 10 atoms

Pure substances made up to of 2 or more types of atoms

Two words in one word

5. A compound contains 6.0 g of carbon and 1.0 g of hydrogen. The percent composition of the compound is:

86% hydrogen and 14% carbon

14% hydrogen and 86% carbon

83% hydrogen and 17% carbon

17% hydrogen and 83% carbon

6. Which of the following method is used to estimate oxygen in an organic compound?

Duma’s method

Combustion method

All of above

K. Jeldahl’s method

7. Which of the following represents an element?

A pure substance made up of two or more types of atoms

A pure substance made up of one type of atom

The periodic table

A compound made up of one type of element

8. The volume occupied by 28 gram of N₂ at STP?

112 Cm³

22.4 dm³

2.24 dm³

1.12 dm³

9. Vapor density of a gas is 22. What is its molecular mass?

10. How can you separate the mixture of two gases of different atomic masses?

Crystallization

Graham’s Law of diffusion

Chromatography

Sublimation

11. Empirical formula of chloroform is

CH₃cl

CH₂C₁₂

CHCl

CHCl₃

12. Copper (II) oxide is mixed with organic compound during combustion. The purpose is

To carry out compete combustion

To reduce the economy of the process

To reduce the time for completion of the reaction

All of these

13. Indicate the incorrect statement form the following

Actual yield is always less than theoretical yield

The empirical and molecular formula of some of the compounds are same

Stoichiometric calculation can only be done if no side reaction happen

A limiting reactant is used at the end of reaction

14. Difference in density is the basis of

Molecular sieving

Gravity separation

Molecular attraction

Ultrafiltration

15. If Na is Avogadro’s number, then number of valence electrons in 4.2 g of nitride ions N³¯ is

3.2 Na

1.6 Na

2.4 Na

4.2 Na

16. One of the substances is used to absorb CO₂ gas in combustion analysis. Which is that substance?

Mg(ClO₄)₂

Al₂O₃

KOH

SiO₂

17. Diameter of an atom is in the range of

2 x10¯¹⁰

0.2 m

0.2 nm

0.2 Pm

18. What is a multivalent ion?

Only negatively charged

Some ions can have only one charge

Ions that are made of more than one type of atom and act as one

An ion that can have more than one charge

19. Most atoms are neutral, to become a positive ion the atom must:

Lose electrons and protons

Gain electrons and protons

Lose electrons

None of these

20. To differentiate between C-12, C-13 and C-14, the instrument that you would use is

Mass spectrometer

Ultraviolet spectrometer

Infra-red spectrometer

Atomic absorption spectrometer

21. What is correct relationship between empirical and molecular formulas?

Empirical formula x √n = Molecular formula

Molecular formula /n = Empirical formula

Empirical formula /n = Molecular formula

Empirical formula x n² = Molecular formula

22. What is a chemical compound?

A combination of two protons and two electrons

A mixture of two or more substance

A combination of two or more chemical elements

A subatomic particle

23. Which of the following is NOT a pure substance?

Soil

Sodium Chloride

Water

Gold

24. The percentage of oxygen in NaOH is

25. 1 mole of CH₄ contains

1.81 x 10²³ molecules of CH₄

4 g-atom of hydrogen

6.02 x 10²³ atoms of H

3.0 g of carbon

Page 2 of 3

26. What is the percent water in hydrated calcium chloride (CaC1₂ 2H₂O)?

32.47%

66.67%

24.51%

12.26%

27. The hydrogen phosphate of certain metal has formula MHPO₄. The formula of metal chloride would be

MC1₃

MC1

MCL₂

M₂C1₂

28. Which of the following statements is FALSE for the chemical equation given below in which nitrogen gas reacts with hydrogen gas to form ammonia gas assuming the reaction goes to completion?
N₂ + 3H₂ → 2NH₃

One moles of N₂ will produce two moles of NH₃.

The reaction of one mole of H₂ will produce 2/3 moles of NH₃.

The reaction of three moles of hydrogen gas will produce 17 g of ammonia

One molecule of nitrogen requires three molecules of hydrogen for complete reaction.

29. Percent of calcium in calcium carbonate is

30%

80%

40%

20%

30. Which of the following is an element?

Sugar

Common Salt

Water

Gold

31. Balance the following equation using minimum integral coefficients: (NH₃ + O₂ → NO₂ + H₂O) Find the stoichiometric coefficient for oxygen gas O₂:

32. Which one of the following is ambiguous?

A mole of potassium ions

A mole of electrons

A mole of hydrogen

A mole of sodium atoms

33. Bromine has two isotopes having the relative abundances as ⁷⁵₃₉Br = 50.51% and ⁸¹₃₅Br= 49.49%. The average atomic mass of bromine is

79.5

34. Which of the following statements is wrong about isotopes?

They possess same position in the periodic table

They possess same physical properties

They possess same chemical properties

They possess different mass number

35. What do you call pure substances that are formed from the attraction between positive ions and negative ions?

Ionic compounds

Ionic atoms

Ionic charges

Ionic element

36. What are the parts of an atom?

Ions, electrons, neutrons, water

Nucleus, element, carbon, space

Protons, neutrons, electrons, nucleus

Protons, neutrons, nucleus, mass

37. Ayesha required an aqueous solution of sodium chloride. She made the solution by dissolving salt in:

Vinegar

Water

Air

Oxygen gas

38. How many moles of KBrO₃ are required to prepare 0.0700 moles of Br₂ according to the reaction: KBrO₃ + 5KBr + 6HNO₃ → 6KNO₃ + 3Br₂ + 3H₂O

0.0233

0.0704

0.0732

0.210

39. The empirical formula of the compound having 50% sulphur and 50% oxygen by mass is

SO₃

SO₂

S₂O₃

40. For which of the following terms empirical formula cannot be applied?

It can be applied to all

H₂O

CC1₄

NaC1

41. How many elements are present in two molecules of aspirin? The formula for aspirin is C₉H₈O₄.

42. If the empirical formula of compound is CH₂. Which of the following is true about its molecular formula?

Only one molecular formula (CH2) is possible

Only one molecular formula (C2H2) is possible

Its molecular formula does not exist

More than one could be a molecular formula for CH₂

43. Which law directly explains the law of conservation of mass?

Dalton’s law

Hund’s rule

Newton’s law

Moley’s law

44. The Number of oxygen atoms in 4.4 g of CO2 is approximately

6 x 10²²

1.2 x 10²³

12 x 10²³

45. Which of the following is NOT true of matter on the Earth?

All matter contains chemical elements

All substances are made of matter

Matter always consists of molecules

Matter is always composed of atoms

46. What are the two different types of ions?

Electrons and protons

Polyatomic and multivalent

Negative and positive

Polyatomic and compound ions

47. Since atoms are neutral, the number of electrons is equal to the number of:

Ions

Protons

Neutrons

Nucleus

48. Among the following pairs, the one which illustrates the law of multiple proportions is

NH₃, HC1

H₂S, SO₂

CuO, Cu₂O

CS₂, FeSO₄

49. The prefix 10¹⁸ is

Kilo

Giga

Nano

Exa

50. Calculate the weight, in grams, of one molecule of carbon dioxide, CO₂.

1.99 x 10¯²³

4.65 x 10¯²³

1.37 x 10²²

7.31 x 10¯²³

Page 3 of 3

51. Molecular compounds can be found in all three states of matter at room temperature. Which molecule compound is a liquid at room temperature?

Sugar

Methane

Water

Carbon dioxide

52. The empirical formula of a compound is CH₂O and its molecular mass is 120. The molecular formula of the compound is

C₃H₆O₃

CH₂O

C₂H₄O₂

C₄H₈O₄

53. Which of the following is a pure substance made up of two or more types of atoms or elements?

Mixture

Element

Compound

Crystal

54. How do you calculate the number of neutrons in an atom?

The atomic mass subtracted the number of electrons

The atomic mass plus the number of electrons

The atomic mass subtracted the number of protons

The atomic mass plus the number of protons

55. The compound having highest percent of oxygen is

CH₃COOH

H₂O

CH₃COCH₃

C₂H₅OH

56. What is the net charge on ferrous ion?

57. A gaseous mixture contains 50% helium and 50% methane by volume. What is the percent by weight of methane in the mixture?

20.05%

50%

19.97%

80.03%

58. How many number of ions are there in 98 grams of sulphate ions?

6.02 x 10²³

6.02 x 10²³ x 2

3 x 6.02 x 10²³

4 x 6.02 x 10²³

59. How will you separate a mixture of two gases?

Osmosis

Chromatography

Fractional distillation technique

Graham’s law of diffusion technique

60. An anhydrous salt of copper is found to contain 52.7% chlorine and 47.3% copper by mass. What is the empirical formula for this salt?

Cu₂Cl₃

CuCl₃

CuCl₂

CuCl

61. Calculate the number of moles of CaCO₃ (Formula weight = 100) in a sample that weighs 25.0 grams.

0.75

1.00

0.5

0.25

62. What does the atomic number of an atom represent?

Protons and neutrons

Neutrons and electrons

Electrons and shells

Protons and electrons

63. How many moles of CO₂ are present in 220 mg?

5 moles

10 moles

0.005 mole

5000 mole

64. What are the ratios among the volumes of gases of ³²O₂,²H₂, and ¹⁶CH₄ if equal mass of each gas is taken?

1:1:1

1:16:2

2:16:2

2:16:1

65. Water (H₂O) is a common compound made up of:

3 elements and a total of 3 atoms

2 elements and a total of 3 atoms

3 elements and a total of 2 atoms

2 elements and a total of 2 atoms

66. How many moles of Helium gas occupy 22.4 L at 0°C at 1 atm. Pressure?

1.11

1.0

0.90

0.11

67. The set of numerical coefficients that balances the chemical equation K₂CrO₄ + CH1 → K₂Cr₂O₇ + KC1 + H₂O

1, 1, 2, 2, 1

2, 2, 1, 2, 1

2, 1, 1, 2, 1

2, 2, 1, 1, 1

68. A ring contains 1.2g of diamond. How many number of carbon atoms are in diamond?

6.02 x 10²³

3.01 x 10²³

6.02 x 10²²

3.01 x 10²²

69. The coefficient of viscosity η of a fluid moving steadily between two surfaces is given by the formula, f = η dV/dx where f is the frictional force on the fluid. A is an area in the fluid and dV/dx is the velocity gradient inside the fluid at that area. The S.I. unit of viscosity coefficient η is given as,

Nm¯²s¯²

Nil, it is dimensionless constant

Kg m¯¹s¯¹

Newton

70. Irrespective of the source, pure sample of water always yields 88.89% mass of oxygen and 11.11% mass of hydrogen. This is explained by the law of

Multiple proportions

Constant volume

Definite proportions

Conservation of mass

71. Which of the following could be an empirical formula?

H₂O₂

C₆H₁₂O₆

BaO₂

C₂H₄

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Maan AliLast Updated: October 14, 2025

33 Comments

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October 26, 2022 at 2:22 pm

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October 26, 2022 at 1:52 pm

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August 13, 2022 at 11:27 am

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October 22, 2020 at 5:26 pm

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October 12, 2020 at 4:43 pm

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Momo says:

December 9, 2018 at 11:24 am

Mass of one mole of iodine is 254g not 245g. (127*2=254g)

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August 25, 2017 at 7:20 pm

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August 20, 2017 at 3:50 pm

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Basic Concepts of Chemistry Online Mcqs Test

Important Basic Concepts of Chemistry Question and Answer

Basic Concepts of Chemistry Practice Test Online With Explanation

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