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

5 moles

5000 mole

0.005 mole

10 moles

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

2 elements and a total of 3 atoms

3 elements and a total of 2 atoms

3 elements and a total of 3 atoms

2 elements and a total of 2 atoms

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

0.75

0.25

0.5

1.00

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

Gold

Water

Soil

Sodium Chloride

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

Atomic absorption spectrometer

Ultraviolet spectrometer

Mass spectrometer

Infra-red spectrometer

6. 1 mole of CH₄ contains

6.02 x 10²³ atoms of H

4 g-atom of hydrogen

3.0 g of carbon

1.81 x 10²³ molecules of CH₄

7. The compound having highest percent of oxygen is

C₂H₅OH

H₂O

CH₃COCH₃

CH₃COOH

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

6.02 x 10²³

6.02 x 10²²

3.01 x 10²²

3.01 x 10²³

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

CC1₄

H₂O

It can be applied to all

NaC1

10. The modern atomic weight scale is based on

H¹

O¹⁶

C¹³

C¹²

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

Sugar

Water

Methane

Carbon dioxide

12. 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

CuCl

CuCl₃

CuCl₂

13. Isotopes differ in the

Number of electrons

Number of protons

Number of atoms

Number of neutrons

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

15. Which of the following is an element?

Common Salt

Sugar

Gold

Water

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

0.0704

0.0732

0.210

0.0233

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

To reduce the time for completion of the reaction

To carry out compete combustion

To reduce the economy of the process

All of these

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

4 x 6.02 x 10²³

3 x 6.02 x 10²³

6.02 x 10²³ x 2

6.02 x 10²³

19. Difference in density is the basis of

Molecular sieving

Ultrafiltration

Molecular attraction

Gravity separation

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

Ions

Neutrons

Nucleus

Protons

21. Indicate the incorrect statement form the following

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

A limiting reactant is used at the end of reaction

Actual yield is always less than theoretical yield

Stoichiometric calculation can only be done if no side reaction happen

22. The prefix 10¹⁸ is

Exa

Kilo

Giga

Nano

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

The atomic mass plus the number of electrons

The atomic mass subtracted the number of electrons

The atomic mass plus the number of protons

The atomic mass subtracted the number of protons

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

SiO₂

Mg(ClO₄)₂

KOH

Al₂O₃

25. The percentage of oxygen in NaOH is

Page 2 of 3

26. 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,

Newton

Kg m¯¹s¯¹

Nil, it is dimensionless constant

Nm¯²s¯²

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

1.0

0.11

1.11

0.90

28. What is the net charge on ferrous ion?

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

14% hydrogen and 86% carbon

83% hydrogen and 17% carbon

86% hydrogen and 14% carbon

17% hydrogen and 83% carbon

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

NH₃, HC1

CS₂, FeSO₄

CuO, Cu₂O

H₂S, SO₂

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

3.2 Na

2.4 Na

4.2 Na

1.6 Na

32. Percent of calcium in calcium carbonate is

30%

20%

80%

40%

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

Moley’s law

Dalton’s law

Newton’s law

Hund’s rule

34. Diameter of an atom is in the range of

0.2 nm

2 x10¯¹⁰

0.2 Pm

0.2 m

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

32.47%

24.51%

12.26%

66.67%

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

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

MC1₃

MC1

M₂C1₂

MCL₂

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

Vinegar

Air

Oxygen gas

Water

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

1:16:2

2:16:2

2:16:1

1:1:1

40. 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

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

None of these

Lose electrons

Lose electrons and protons

Gain electrons and protons

42. 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

Conservation of mass

Definite proportions

43. Which one of the following is ambiguous?

A mole of hydrogen

A mole of sodium atoms

A mole of potassium ions

A mole of electrons

44. 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%

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

SO₃

S₂O₃

SO₂

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

Molecular formula /n = Empirical formula

Empirical formula x √n = Molecular formula

Empirical formula /n = Molecular formula

Empirical formula x n² = Molecular formula

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

All matter contains chemical elements

Matter is always composed of atoms

All substances are made of matter

Matter always consists of molecules

48. What are the two different types of ions?

Polyatomic and compound ions

Electrons and protons

Negative and positive

Polyatomic and multivalent

49. What is a multivalent ion?

Only negatively charged

An ion that can have more than one charge

Some ions can have only one charge

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

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

K. Jeldahl’s method

Combustion method

Duma’s method

All of above

Page 3 of 3

51. 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

More than one could be a molecular formula for CH₂

Only one molecular formula (C2H2) is possible

Its molecular formula does not exist

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

53. 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, 2, 1, 1, 1

2, 1, 1, 2, 1

54. Which of the following represents a compound?

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

A pure substance made up of one type of atom

Two words in one word

Made up of 10 atoms

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

Crystal

Element

Compound

Mixture

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

Ionic compounds

Ionic charges

Ionic atoms

Ionic element

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

Neutrons and electrons

Protons and neutrons

Protons and electrons

Electrons and shells

58. 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

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

7.31 x 10¯²³

1.99 x 10¯²³

4.65 x 10¯²³

1.37 x 10²²

60. Which of the following represents an element?

A pure substance made up of one type of atom

The periodic table

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

A compound made up of one type of element

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

C₂H₄O₂

CH₂O

C₄H₈O₄

C₃H₆O₃

62. 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.

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

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

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

Chromatography

Fractional distillation technique

Osmosis

Graham’s law of diffusion technique

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

H₂O₂

C₂H₄

C₆H₁₂O₆

BaO₂

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

They possess different mass number

They possess same physical properties

They possess same chemical properties

They possess same position in the periodic table

66. Empirical formula of chloroform is

CHCl₃

CH₂C₁₂

CH₃cl

CHCl

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

112 Cm³

2.24 dm³

1.12 dm³

22.4 dm³

68. What are the parts of an atom?

Protons, neutrons, electrons, nucleus

Protons, neutrons, nucleus, mass

Ions, electrons, neutrons, water

Nucleus, element, carbon, space

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

Sublimation

Crystallization

Graham’s Law of diffusion

Chromatography

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

6 x 10²²

1.2 x 10²³

12 x 10²³

6 x 10²²

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

NO₂

N₂O

N₂O₃

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Maan AliLast Updated: October 14, 2025

33 Comments

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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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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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