Chemistry MCQ Questions with Answer for all Competitive Exams

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Chemistry MCQ Questions with Answer

Q41. The water pollution in the river is measured by the dissolved amount of

(a) Chlorine

(b) Ozone

(c) Nitrogen

(d) Oxygen

Answer: (d)

Explanation: Water pollution in the river or any other water body is measured by the amount of dissolved oxygen. Water pollution can be measured on the basis of parameters like dirtiness, change in texture, total suspended solids, and other important factors like,

1. A decrease in dissolved oxygen (DO) (concentration of dissolved oxygen in water samples).
2. An increase in BOD, (Biochemical Oxygen Demand) is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period.
3. An increase in COD, (Chemical Oxygen Demand) test is commonly used to indirectly measure the number of organic compounds in water.

Q42. Solder is an alloy of

​(a) ​Tin and lead

​(b) ​Tin and copper ​

(c)​ Tin, copper, and zinc ​

(d)​ Tin, lead, and zinc

Answer: ​(a)​

Explanation: Solders are typically made from tin or lead or a combination of both in the

Q43. Which one of the following noble gases are not found in the atmosphere? ​

(a)​ Argon ​

(b)​ Krypton ​

(c)​ Radon ​

(d)​ Xenon

Answer: ​(c)​

Explanation: All noble gases are present in Earth’s atmosphere except for helium and radon. Noble gases are a group of highly unreactive elements placed in the Gr-18 (VIIIB) in the periodic table.

Q44. Atomic size is of the order of—

(a) 10 –8 cm

(b) 10 –10 cm

(c) 10 –13 cm

(d) 10 –6 cm

Answer: (a)

Explanation: Atomic size is of the order of 10 –10 m or 10 –8 cm. Atomic size is the distance from the nucleus to the Valence Shell (outermost shell) of an atom.

Q45. Which of the following has the lowest frequency?

(a) Visible light

(b) Gamma rays

(c) X-rays

(d) Ultraviolet rays

Answer: (a)

Explanation: The different types of radiations are arranged in the decreasing order of frequencies or increasing order of wavelength as Cosmic rays, Gamma rays, X-rays, Ultraviolet radiations, visible radiations, Infrared radiations, Microwaves, and Radio waves.

Q46. All isotopes of the same element have —

(a) Different atomic numbers and different atomic mass

(b) Different atomic numbers and the same atomic mass

(c) The same atomic number but a different atomic mass

(d) The same atomic number and the same atomic mass

Answer: (c)

Explanation: Atoms of an element having the same atomic number but having different mass numbers are known as isotopes. e.g. 1H1, 1H2, 1H3

Q47. Which one of the following pairs of materials serves as electrodes in chargeable batteries commonly used in devices such as torchlight, electric shaver, etc.?

(a) Nickel and cadmium

(b) Zinc and carbon

(c) Lead peroxide and lead

(d) Iron and cadmium

Answer: (a)

Explanation: Ni-Cd batteries contain nickel hydroxide as a positive electrode plate, a cadmium hydroxide as a negative electrode plate, and an alkaline electrolyte as a separator. The chemical reaction which occurs in Ni-Cd battery is

2NiO(OH) + Cd + 2HO2 ↔ Ni(OH) + Cd(OH)

Q48. Assertion (A): Large cold storage plants use ammonia as refrigerant while domestic refrigerators use chlorofluorocarbons.

Reason (R): Ammonia can be liquefied at ambient temperature and low pressure.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is NOT a correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

Answer: (a)

Explanation: Ammonia is used as a large-scale refrigerant because it has the highest refrigerating capacity per pound of any refrigerant and a number of other excellent thermal properties that make it popular for a number of refrigeration applications in spite of its being toxic, explosive, and flammable within certain conditions. Ammonia is used as refrigerant prominently in the refrigeration systems of the food industry like dairies, ice creams plants, frozen food production plants, cold storage warehouses, processors of fish, meat, and a number of other applications. Comparatively chlorofluorocarbon (CFC) chemical, safer refrigerators were possible for home and consumer use.

Q49. In an atom, the order of filling up of the orbitals is governed by—

(a) Aufbau principle

(b) Heisenberg’s uncertainty principle

(c) Hund’s rule

(d) Pauli’s exclusion Principle

Answer: (a)

Explanation: According to the Aufbau principle in the ground state of the atoms, the orbitals are filled in order of their increasing order of energy.

Q50. The phenomenon of Radioactivity was discovered by –

(a) Becquerel

(b) Rutherford

(c) Curle

(d) Suri

Answer: (a)

Explanation: Radioactivity was discovered by Henri Becquerel (1895-96). For work in this field he, along with Marie Sklodowska-Curie and Pierre Curie, received the 1903 Nobel Prize in Physics.

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