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General ScienceMediumAsked in: UPSC CAPF · CAPF 2026, Paper I

Which one of the following processes is not used for the production of hydrogen gas?

  1. A.Electrolytic process
  2. B.Water gas-steam process
  3. C.Liquefaction of coal gas
  4. D.Hydrolysis of calcium carbide

Correct answer

D. Hydrolysis of calcium carbide

Explanation

The correct answer is D, Hydrolysis of calcium carbide. When calcium carbide reacts with water it gives acetylene (ethyne) gas and calcium hydroxide, not hydrogen.

The reaction CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂ is the old method of making acetylene, once burnt in miners' lamps and still used for welding and for ripening fruit illegally. Hydrogen, on the other hand, is made in industry by passing steam over red-hot coke and then over a catalyst (the water gas and steam shift route), by electrolysis of water or brine, and from coal gas, where cooling liquefies the other gases and leaves hydrogen behind.

A is wrong because electrolysis of acidified water gives hydrogen at the cathode, and it is the route for very pure or green hydrogen. B is wrong because the water gas reaction followed by the steam shift is a main commercial source of hydrogen. C is wrong because liquefying coal gas separates out hydrogen, which stays a gas at the lowest temperatures.

Exam tip: calcium carbide + water = acetylene; steam + red-hot coke = water gas (CO + H₂).

Practice Questions

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Q1.General ScienceAsked in: UPSC Civil Services · CSE Prelims 2017, GS Paper IMedium

Consider the following pairs : (Commonly used / consumed materials : Unwanted or controversial chemicals likely to be found in them) 1. Lipstick : Lead 2. Soft drinks : Brominated vegetable oils 3. Chinese fast food : Monosodium glutamate Which of the pairs given above is/are correctly matched ?

  1. A.1 only
  2. B.2 and 3 only
  3. C.1 and 3 only
  4. D.1, 2 and 3
Show answer
Correct answer: D. 1, 2 and 3

Each product has been linked to the chemical paired with it. Lead has been found as a trace contaminant in many lipsticks, coming from colour pigments; since lipstick is swallowed in small amounts, regular use raises concern because lead is a toxic heavy metal that harms the nervous system.

Q2.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is not true for anodizing process?

  1. A.It makes aluminium corrosion resistant.
  2. B.Metals like aluminium, titanium and magnesium can be anodized.
  3. C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
  4. D.It is used in aircraft industry.
Show answer
Correct answer: C. Clean aluminium article is the anode and oxygen gas is evolved at the cathode.

In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.

Q3.General ScienceAsked in: CDS · CDS-II 2016, GKMedium

Which one of the following statements is not correct?

  1. A.The response of the ear to sound of increasing intensity is approximately logarithmic.
  2. B.The sensitivity of the human ear does not vary with the frequency of the sound.
  3. C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
  4. D.Longitudinal waves can travel in all media—solids, liquids and gases.
Show answer
Correct answer: B. The sensitivity of the human ear does not vary with the frequency of the sound.

The statement that the sensitivity of the human ear does not vary with frequency is false, because the ear is far more sensitive to some frequencies than to others.

Q4.General ScienceAsked in: CDS · CDS-I 2017, GKEasy

Kwashiorkor disease in children is caused by

  1. A.sufficient carbohydrates but less fats in diet
  2. B.sufficient carbohydrates and fats but deficient proteins in diet
  3. C.sufficient vitamins but deficient fats in diet
  4. D.sufficient fats but deficient vitamins in diet
Show answer
Correct answer: B. sufficient carbohydrates and fats but deficient proteins in diet

Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.

Q5.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is the correct order of pH for the given substances?

  1. A.Coffee < Lemon juice < Milk of magnesia < Blood
  2. B.Milk of magnesia < Blood < Coffee < Lemon juice
  3. C.Lemon juice < Blood < Coffee < Milk of magnesia
  4. D.Lemon juice < Coffee < Blood < Milk of magnesia
Show answer
Correct answer: D. Lemon juice < Coffee < Blood < Milk of magnesia

Arranged from most acidic to most basic, the four substances fall in exactly this order. Lemon juice, rich in citric acid, has a pH of about 2 to 2.5.