Chemistry MCQs Set 4 Frequently Asked Questions in Exams

This section contains chemistry MCQs designed to test your chemistry knowledge and aid in your preparation for competitive exams. Practicing these questions enhances comprehension of fundamental chemistry concepts and boosts exam performance. It’s worth noting that these questions are frequently asked in various exams, making them an excellent resource for exam preparation.

1. What encompasses the essence of chemistry?
a. Internal structural changes in matter
b. Composition of matter
c. Properties of matter
d. Composition and properties of matter
Answer: d. Composition and properties of matter

2. What is the radioactive isotope of hydrogen known as?
a. Tritium
b. Deuterium
c. Protium
d. Ortho-hydrogen
Answer: a. Tritium

3. Who discovered the electron?
a. Michael Faraday
b. James Maxwell
c. Yuri Gagarin
d. J.J. Thomson
Answer: d. J.J. Thomson

4. Sodium carbonate is produced by which process?
a. Haber process
b. Ammonia Solvay process
c. Decons process
d. Lead chamber process
Answer: b. Ammonia Solvay process

5. Which among the following is a substance?
a. Brass
b. Tape water
c. Graphite
d. Sand
Answer: c. Graphite

6. Substances conducting electricity in both solid and liquid states are generally:
a. Ionic substances
b. Metallic substances
c. Molecular solids
d. Covalent network solids
Answer: b. Metallic substances

7. Covalent network crystals generally possess:
a. Higher melting point than molecular crystals
b. Lower melting point than molecular crystals
c. Discrete molecules linked by Van der Waals forces
d. Hydrogen bonding
Answer: a. Higher melting point than molecular crystals

8. What is the mixture of Potassium Nitrate, Powdered Charcoal, and Sulphur called?
a. Paint
b. Glass
c. Gun Powder
d. Cement
Answer: c. Gun Powder

9. What is the approximate diameter range of an atom?
a. 0.2 meters
b. 0.2 millimeters
c. 0.2 nanometers
d. 0.2 picometers
Answer: c. 0.2 nanometers

10. What does a mass spectrometer determine besides the Mass number of isotopes?
a. Atomic number
b. Relative abundance
c. Electronic configuration
d. All of the above
Answer: b. Relative abundance

11. What does the number of peaks obtained in mass spectrometry indicate?
a. Relative abundance
b. Average mass of element
c. Number of isotopes
d. Relative isotopic mass
Answer: c. Number of isotopes

12. What is the empirical formula of chloroform?
a. CH2 C12
b. CH3C1
c. CC14
d. CHCL3
Answer: d. CHCL3

13. When referring to the molecular mass of water (18g), what does it mean?
a. 1-mole molecules of water
b. 1-gram molecule of water
c. 3-gram atoms
d. All of these
Answer: a. 1-mole molecules of water

14. What does one mole of CO2 contain?
a. 6.022 × 10^23 molecules
b. 44 grams
c. 12 grams of carbon
d. 22.4 liters at STP
Answer: a. 6.022 × 10^23 molecules

15. How many isotopes do elements with even mass numbers and even atomic numbers generally have?
a. 280
b. 300
c. 154
d. 54
Answer: c. 154

16. Which term is not used for ionic compounds?
a. Formula unit
b. Empirical formula
c. Molecular formula
d. Formula mass
Answer: c. Molecular formula

17. Among the following elements, which has the maximum number of isotopes?
a. Oxygen
b. Carbon
c. Tin
d. Chlorine
Answer: c. Tin

18. What is the percentage of calcium in calcium carbonate?
a. 80%
b. 30%
c. 40%
d. 20%
Answer: c. 40%

19. What volume is occupied by 2.8 g of N2 at STP (Standard Temperature and Pressure)?
a. 4.48 dm³
b. 44.8 dm³
c. 2.24 dm³
d. 22.4 dm³
Answer: c. 2.24 dm³

20. How many moles of CO2 contain 20 g of oxygen?
a. 0.25
b. 0.5
c. 0.62
d. 1.62
Answer: c. 0.62
Explanation: Calculate the molar mass of oxygen:
Molar mass of O = 16.00 g/mol
Determine the number of moles of oxygen:
Number of moles of O = Mass / Molar mass
Number of moles of O = 20 g / 16.00 g/mol = 1.25 mol
CO2 contains 2 oxygen atoms per molecule.
Calculate the number of moles of CO2:
Number of moles of CO2 = Number of moles of O / 2
Number of moles of CO2 = 1.25 mol / 2 = 0.625 mol
Therefore, the correct answer closest among the provided options is C. 0.62.

21. How many isotopes possess an odd atomic number?
a. 154
b. 280
c. 86
d. 300

22. Why do most elements exhibit fractional atomic masses?
a. The fractional mass of protons and neutrons
b. The presence of multiple isotopes
c. Diverse molecular structures
d. Incomplete atomic weights
Answer: b. The presence of multiple isotopes

23. Which among the following substances does not qualify as a macromolecule?
a. Protein
b. Hemoglobin
c. Diamond
d. Sucrose
Answer: d. Sucrose

24. What is the equivalent value of 1 atomic mass unit (amu)?
a. 1.6 x 10^-27 g
b. 1.6 x 10^-24 g
c. 1.6 x 10^-26 g
d. 1.6 x 10^-28 g
Answer: b. 1.6 x 10^-24 g

25. Identify the isoelectronic species from the following options:
a. H+ H H-
b. Li+ Na+ K+
c. Cl- Br- I
d. F- Ne Na+
Answer: d. F- Ne Na+

26. Identify the ion formation process that is always exothermic:
a. Uni-negative
b. Uni-positive
c. Di-negative
d. Di-positive
Answer: a. Uni-negative

27. Identify the element that is NOT mono-isotopic from the options provided:
a. Arsenic
b. Uranium
c. Iodine
d. Nickel
Answer: b. Uranium

28. The mass of one decimole of electrons (NA) is:
a. 1.008 mg
b. 0.184 mg
c. 0.054 mg
d. 5.4 mg
Answer: c. 0.054 mg
Explanation: The mass of one electron is approximately 9.11 × 10-31 kg. The mass of 1 mole of electrons is: 9.11 × 10-31 kg/electron * 6.022 × 1023 electrons/mole = 5.486 × 10-4 kg/mole
The mass of 1 decimole of electrons is: 5.486 × 10-4 kg/mole * 1/10 = 5.486 × 10-5 kg This is approximately 54.86 × 10-6 g. To convert g to mg, multiply by 1000. 54.86 × 10-6 g * 1000 mg/g = 0.05486 mg.
So, the correct answer is 0.054 mg.

29. Choose the incorrect statement regarding isotopes:
a. They possess different mass numbers
b. They possess different positions in the periodic table
c. They possess different physical properties
d. They possess the same chemical properties
Answer: b. They possess different positions in the periodic table

30. For which purpose is qualitative analysis primarily conducted?
a. Determining quantities of elements in a sample
b. Identifying elements present in a sample
c. Measuring the exact mass of compounds
d. Calculating the molecular weights of compounds
Answer: b. Identifying elements present in a sample

31. What is the primary objective of combustion analysis in chemistry?
a. To determine the Molecular mass
b. To determine the Empirical formula
c. To determine the Molecular formula
d. To determine the Formula mass
Answer: b. To determine the Empirical formula

32. Identify the method used to estimate hydrogen in an organic compound:
a. Dumas method
b. Kjeldahl’s method
c. Fusion method
d. Combustion method
Answer: d. Combustion method

33. What will the nucleus of an atom of every element always contain?
a. Neutrons and electrons
b. Protons and electrons
c. Protons and neutrons
d. Protons and positrons
Answer: c. Protons and neutrons

34. When 1 mole of phosphoric acid is dissolved in an aqueous solution, how many moles of negative and positive ions are collected in total?
a. 2
b. 2.5
c. 3
d. 1.5
Answer: c. 3

35. Dempster’s mass spectrometer consists of how many zones or parts?
a. Four
b. Five
c. Seven
d. Three
Answer: b. Five

36. Which of the following variables is not used to describe gases?
a. Pressure
b. Volume
c. Density
d. Moles
Answer: c. Density

37. In which of the following applications is methyl alcohol not used?
a. As a solvent
b. As an anti-freezing agent
c. As a substitute for petrol
d. For denaturing of ethyl alcohol
Answer: c. As a substitute for petrol

38. Under the same conditions of temperature and pressure, if oxygen (molecular weight = 32) diffuses at a rate of 10 cm³/min, how quickly will hydrogen (molecular weight = 2) diffuse?
a. 30 cm³/min
b. 40 cm³/min
c. 160 cm³/min
d. 140 cm³/min
Answer: b. 40 cm³/min
Explanation: According to Graham’s law of diffusion, the rate of diffusion of gases is inversely proportional to the square root of their molecular weights.
Rate of Hydrogen = √(Oxygen Molecular Weight / Hydrogen Molecular Weight) * Oxygen Diffusion Rate
Rate of Hydrogen = √(32 / 2) * 10 cm³/min
Rate of Hydrogen = 4 * 10 cm³/min
Rate of Hydrogen = 40 cm³/min

39. Which of the following changes does not occur as a substance transitions from a solid to a liquid?
a. Alteration in molecular arrangement
b. Decrease in kinetic energy of the molecules
c. Modification in intermolecular forces
d. Increased frequency of molecular movement
Answer: b. Decrease in kinetic energy of the molecules

40. Rectified spirit alcohol typically contains a high percentage of…?
a. 95% alcohol
b. 90% alcohol
c. 85% alcohol
d. 100% alcohol
Answer: a. 95% alcohol

41. How many isomers are possible for butyl chloride?
a. Four
b. Five
c. Seven
d. Three
Answer: a. Four

42. Metallic crystals are soluble in which of the following?
a. Polar solvent
b. Nonpolar solvent
c. Aqueous solution of acids
d. Fused metal
Answer: d. Fused metal

43. The instrument used to measure the paramagnetic behavior of a substance is…?
a. Faraday’s balance
b. Sensitive torsion balance
c. Guoy’s balance
d. Para Magnetometer
Answer: c. Guoy’s balance

44. When an electron moves with a velocity of 1.5 × 10^6 m/s in the first orbit of Bohr’s model of hydrogen, calculate the de Broglie wavelength of the electron:
a. 0.177
b. 0.994
c. 0.348
d. 0.485
Answer: d. 0.485
Explanation: Given:
Velocity of the electron (v) = 1.5 × 10^6 m/s
Mass of the electron (m) = 9.11 × 10^-31 kg
Planck’s constant (h) = 6.63 × 10^-34 Js
Formula: De Broglie wavelength (λ) = h / (mv)
λ = (6.63 × 10^-34 Js) / ((9.11 × 10^-31 kg) × (1.5 × 10^6 m/s))
λ ≈ 0.485 nm
Therefore, the de Broglie wavelength of the electron is approximately 0.485 nanometers.

45. Upon treating methyl iodide and ethyl iodide with sodium metal, what are the major products formed?
a. Methane and ethane
b. Ethane and propane
c. Ethene and propene
d. Ethyne and butane
Answer: b. Ethane and propane

46. Which of the following is classified as a mineral fiber?
a. Asbestos
b. Teflon
c. Saran
d. Acrylic
Answer: a. Asbestos

47. Which among the following substance is considered the hardest?
a. Graphite
b. Diamond
c. Moissanite
d. Silicon carbide
Answer: b. Diamond

48. Which of the following solids does not primarily consist of covalent bonds?
a. Graphite
b. Diamond
c. Moissanite
d. Copper
Answer: d. Copper

49. Which of these is not a characteristic of a reversible reaction?
a. Incomplete conversion of reactants to products
b. Catalyst altering the reaction direction
c. Establishment of chemical equilibrium
d. Decrease in the forward reaction rate as the reaction progresses
Answer: b. Catalyst altering the reaction direction

50. What is the concentration of H+ ions in a solution with a pH of 0?
a. 1 × 10^0 mol/L
b. 1 × 10^-3 mol/L
c. 1 × 10^-1 mol/L
d. 1 × 10^2 mol/L
Answer: a. 1 × 10^0 mol/L