Q1. One litre of cold air weighs heavier than the dry air (1 Lit) because of the
(a) Increased number of collisions between the molecules
(b) Increased number of molecules at low temperature
(c) Greater energy of molecules at high temperature
(d) Lower energy of molecules at high temperature
Answer: (b) Increased number of molecules at low temperature
Explanation: Cold air is denser because molecules move slower and pack more tightly together, increasing the number of molecules per unit volume. This results in greater mass per litre, making cold air heavier than warm or dry air.
Q2. Why is it easier to cook in a pressure cooker ?
(a) High pressure creates turbulence
(b) More steam is formed inside the cooker
(c) Boiling point of water is raised
(d) Boiling point of water is lowered
(UPSC Prelims 1981)
Answer: (c) Boiling point of water is raised
Explanation: In a pressure cooker, the pressure increases, which raises the boiling point of water. This allows food to cook at a higher temperature, speeding up the process and making it more efficient.
