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

Water

Oxygen gas

Vinegar

Air

2. Indicate the incorrect statement form the following

A limiting reactant is used at the end of reaction

Stoichiometric calculation can only be done if no side reaction happen

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

Actual yield is always less than theoretical yield

3. Which of the following represents a compound?

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

Two words in one word

A pure substance made up of one type of atom

Made up of 10 atoms

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

66.67%

12.26%

24.51%

32.47%

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

Osmosis

Chromatography

Fractional distillation technique

Graham’s law of diffusion technique

6. What is a multivalent ion?

An ion that can have more than one charge

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

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

Compound

Mixture

Crystal

Element

8. 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

9. The compound having highest percent of oxygen is

C₂H₅OH

CH₃COOH

H₂O

CH₃COCH₃

10. What are the two different types of ions?

Electrons and protons

Negative and positive

Polyatomic and compound ions

Polyatomic and multivalent

11. 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,

Nil, it is dimensionless constant

Nm¯²s¯²

Newton

Kg m¯¹s¯¹

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

6.02 x 10²³ x 2

6.02 x 10²³

3 x 6.02 x 10²³

4 x 6.02 x 10²³

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

5 moles

10 moles

0.005 mole

5000 mole

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

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

2, 2, 1, 1, 1

2, 1, 1, 2, 1

1, 1, 2, 2, 1

2, 2, 1, 2, 1

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

Soil

Gold

Water

Sodium Chloride

17. What is the net charge on ferrous ion?

18. What is a chemical compound?

A combination of two protons and two electrons

A combination of two or more chemical elements

A mixture of two or more substance

A subatomic particle

19. Percent of calcium in calcium carbonate is

80%

20%

30%

40%

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

3.01 x 10²³

3.01 x 10²²

6.02 x 10²³

6.02 x 10²²

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

Gain electrons and protons

Lose electrons

None of these

Lose electrons and protons

22. 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 three moles of hydrogen gas will produce 17 g of ammonia

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.

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

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

C₂H₄O₂

C₃H₆O₃

C₄H₈O₄

CH₂O

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

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

The atomic mass plus the number of electrons

The atomic mass plus the number of protons

The atomic mass subtracted the number of protons

The atomic mass subtracted the number of electrons

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

To reduce the economy of the process

All of these

To carry out compete combustion

To reduce the time for completion of the reaction

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

2 elements and a total of 3 atoms

2 elements and a total of 2 atoms

3 elements and a total of 2 atoms

3 elements and a total of 3 atoms

29. 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?

CuCl₂

Cu₂Cl₃

CuCl

CuCl₃

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

4.65 x 10¯²³

1.37 x 10²²

1.99 x 10¯²³

7.31 x 10¯²³

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

Sublimation

Graham’s Law of diffusion

Crystallization

Chromatography

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

CC1₄

It can be applied to all

H₂O

NaC1

33. Diameter of an atom is in the range of

0.2 nm

0.2 Pm

2 x10¯¹⁰

0.2 m

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

1.12 dm³

22.4 dm³

112 Cm³

2.24 dm³

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

S₂O₃

SO₃

SO₂

36. 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

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

Ionic atoms

Ionic compounds

Ionic charges

Ionic element

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

Protons and electrons

Neutrons and electrons

Protons and neutrons

Electrons and shells

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

They possess same chemical properties

They possess same physical properties

They possess same position in the periodic table

They possess different mass number

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

2:16:2

1:16:2

2:16:1

1:1:1

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

NH₃, HC1

CuO, Cu₂O

CS₂, FeSO₄

H₂S, SO₂

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

Mg(ClO₄)₂

SiO₂

Al₂O₃

KOH

43. The modern atomic weight scale is based on

H¹

O¹⁶

C¹³

C¹²

44. 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

0.0732

0.210

0.0704

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

50%

19.97%

80.03%

20.05%

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

N₂O₃

N₂O

NO₂

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

0.5

1.00

0.75

0.25

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

Matter always consists of molecules

Matter is always composed of atoms

All substances are made of matter

All matter contains chemical elements

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

Combustion method

All of above

Duma’s method

K. Jeldahl’s method

50. The percentage of oxygen in NaOH is

Page 3 of 3

51. 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

52. The prefix 10¹⁸ is

Giga

Kilo

Exa

Nano

53. Which one of the following is ambiguous?

A mole of potassium ions

A mole of sodium atoms

A mole of hydrogen

A mole of electrons

54. What are the parts of an atom?

Protons, neutrons, nucleus, mass

Ions, electrons, neutrons, water

Protons, neutrons, electrons, nucleus

Nucleus, element, carbon, space

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

Hund’s rule

Moley’s law

Newton’s law

Dalton’s law

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

83% hydrogen and 17% carbon

17% hydrogen and 83% carbon

14% hydrogen and 86% carbon

86% hydrogen and 14% carbon

57. Which of the following is an element?

Sugar

Water

Gold

Common Salt

58. Difference in density is the basis of

Gravity separation

Ultrafiltration

Molecular sieving

Molecular attraction

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

Molecular formula /n = Empirical formula

Empirical formula x n² = Molecular formula

Empirical formula /n = Molecular formula

Empirical formula x √n = Molecular formula

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

1.6 Na

3.2 Na

4.2 Na

2.4 Na

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

BaO₂

C₂H₄

H₂O₂

C₆H₁₂O₆

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

0.11

1.0

1.11

0.90

63. 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

Constant volume

Multiple proportions

Definite proportions

Conservation of mass

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

Mass spectrometer

Ultraviolet spectrometer

Atomic absorption spectrometer

Infra-red spectrometer

65. Empirical formula of chloroform is

CHCl₃

CHCl

CH₃cl

CH₂C₁₂

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

Carbon dioxide

Water

Sugar

Methane

67. Which of the following represents an element?

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

The periodic table

A pure substance made up of one type of atom

A compound made up of one type of element

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

Ions

Protons

Neutrons

Nucleus

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

Only one molecular formula (C2H2) is possible

Only one molecular formula (CH2) is possible

More than one could be a molecular formula for CH₂

Its molecular formula does not exist

70. Isotopes differ in the

Number of atoms

Number of neutrons

Number of electrons

Number of protons

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

MC1₃

M₂C1₂

MC1

MCL₂

Complete Guide for Basic Concepts of Chemistry Online Mcqs Test

Basic Concepts of Chemistry Online Mcqs Test is a crucial part of the selection process for government jobs and entrance exams. This online test allows you to practice without any cost.

Why Take This Test?

We have compiled these questions from past papers of PPSC, FPSC, NTS, and OTS. By attempting this quiz, you will:

Understand the difficulty level of the actual exam.
Identify your weak areas in General Knowledge and Current Affairs.

Note: At the end of the quiz, you will see a detailed result card with the correct answers.

33 Comments

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October 26, 2022 at 1:52 pm

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October 22, 2020 at 12:10 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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Important Basic Concepts of Chemistry Question and Answer

Basic Concepts of Chemistry Practice Test Online With Explanation

Complete Guide for Basic Concepts of Chemistry Online Mcqs Test

Why Take This Test?

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