Q1. When iron rusts, the weight
(a) Increases
(b) Decreases
(c) Remains the same
(d) First increases then decreases
(UPSC Prelims 1980)
Answer: (a) Increases
Explanation: Rusting is a chemical reaction where iron combines with oxygen, forming iron oxide, which adds mass, causing the weight to increase.
Q2. What is the difference between an explosion and combustion?
(a) In the former nuclear reaction takes place while in the latter case burning takes place
(b) In the former chemical energy is transformed into nuclear energy while in the latter case the chemical energy is transformed into heat energy
(c) In the former it is violent and rapid reaction with release of much heat energy while in the latter case it is generally slow reaction with release of less heat energy
(d) None of the above
(UPSC Prelims 1983)
Answer: (c) In the former it is violent and rapid reaction with release of much heat energy while in the latter case it is generally slow reaction with release of less heat energy
Explanation: An explosion is a sudden, violent reaction that releases large amounts of energy rapidly, while combustion is a slower, controlled burning process. The key difference lies in the rate and intensity of energy release.
Q3. Urea is prepared by the chemical reaction of
(a) Ammonia and Carbon dioxide
(b) Ammonium sulphate and calcium chloride
(c) Acetamide and ethyl alcohol
(d) Chlorine and water
(UPSC Prelims 1987)
Answer: (a) Ammonia and Carbon dioxide
Explanation: Urea (NH₂CONH₂) is synthesized by reacting ammonia (NH₃) with carbon dioxide (CO₂) under high pressure and temperature. This process is known as the Bosch-Meiser urea process.