Chemistry (CDS-Solved Paper)

Total Questions: 50

31. Which one of the following can extinguish fire more quickly? [Evening Shift-2018 (II)]

Correct Answer: (b) Boiling water
Solution:

Boiling water can extinguish fire more quickly because the process of fire extinguishing involves absorption of heat. Absorption of heat in converting hot water to steam is more than the heat absorbed in heating cold water to the boiling temperature. Hence, boiling water can extinguish fire more quickly than ice, cold water and hot water.

32. Bright light is found to emit from photographer’s flashgun. Thus brightness is due to the presence of which one of the following noble gases? [Morning Shift-2018 (I)]

Correct Answer: (b) Xenon
Solution:

Xenon is used in high intensity photographic flash gun. Xenon can produce a brighter whiter light than other noble gases and tend to have a longer life span.

33. Which one of the following is not a characteristic of a compound? [Morning Shift-2018 (I)]

Correct Answer: (b) All particles of compound are of only one type.
Solution:

A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion

34. Which of the following substances cause temporary hardness in water? [Morning Shift-2018 (I)]

Select the correct answer using the codes given below.

Correct Answer: (d) 1 and 2
Solution:

Temporary hardness in water is due to the presence magnesium and calcium hydrogen carbonates [Mg(HCO₃) and Ca(HCO₃)]₂. It can be removed by boiling and Clark’s method

35. Which one of the following elements will be an isobar of calcium, if the atomic number of calcium is 20 and its mass number is 40? [Morning Shift-2018 (I)]

Correct Answer: (d) Element with 18 protons and 22 neutrons
Solution:

Atoms of different elements having same mass number(A) but different atomic number (Z) are termed as isobars. Element with 18 protons and 22 neutrons is isobaric with calcium as both of them have same mass number.
Mass number of calcium = 40
Mass number of element = number of protons + number of neutrons
= 18 + 22 = 40

36. Which one of the following elements is used as a timekeeper in atomic clocks ? [Morning Shift-2018 (I)]

Correct Answer: (b) Caesium
Solution:

Caesium is used as a timekeeper in atomic clocks. The caesium atomic clocks are very accurate. In principle, they provide portable standard. The national standard of time interval ‘second’ as well as the frequency is maintained through four caesium atomic clocks.

37. Which one of the following gases dissolves in water to give acidic solution? [Morning Shift-2018 (I)]

Correct Answer: (a) Carbon dioxide
Solution:

Carbon dioxide dissolve in water to form acidic solution. Aqueous solution of carbon dioxide is called carbonic acid (H₂CO₃).

38. Consider the following chemical reaction, [Morning Shift-2018 (I)]


In the balanced chemical equation of the above, which of the following will be the values
of the coefficients a, b, c, and d respectively?

Correct Answer: (b) 1, 3, 2, 3
Solution:

A balanced chemical equation involves equal number of atoms of each element an both sides. The balanced chemical equation is given below and its coefficients a,b,c,d are 1,3,2,3.

39. Pearl is a hard object produced within the soft tissues of a mollusk. Which one of the following is the main constituent of pearl? [Evening Shift-2017 (II)]

Correct Answer: (a) Calcium carbonate
Solution:

The soft tissue of mollusc animal accumulateCaCO₃ which makes the pearl in them.

40. In the reaction between hydrogen sulphate ion and water HSO⁻₄ + H₂O → H₃O⁺ + SO₄²⁻ the water acts as

Correct Answer: (b) a base
Solution:

In the given reaction the water acts as a base. A base is a substance which can accept protons or any chemical compound that yields hydroxide ions (OH⁻) in solution.
It is also commonly referred to as any substance that can react with an acid to decrease or neutralise its acidity to form salts and promote certain chemical reactions.