Question

Assertion: As temperature increases, the viscosity of gas increases.
Reason: In gas, molecular momentum transfer is predominated by the cohesive forces.
(a) Both, Assertion and Reason, are true and Reason is the correct explanation of Assertion.
(b) Both, Assertion and Reason, are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.

Answer 1

Hint: In this type of question, we have to check for the statement given and the reason for the given statement is right or wrong and also for the correct explanation. We will use the concept of viscosity of gas, cohesive forces and molecular momentum transfer.

Complete answer:
In a gas, we know that molecular momentum transfer is predominated by the cohesive forces. Cohesive forces are the intermolecular attractive force acting between two adjacent gas molecules. When the gas molecules inside the gas collide with other gas molecules and the momentum of these molecules transfer to those molecules.

According to the Kinetic theory of gases, when the temperature of the gas increases, the randomness of the gas molecules due to molecular momentum transfer exchange increases and this increases the viscosity of the gas.Thus, As temperature increases, the viscosity of gas increases because molecular momentum transfer is predominated by the cohesive forces.

Hence, option A is correct.

Note: The gas viscosity will increase with temperature. According to the kinetic theory of gases, viscosity of gas is proportional to the square root of the absolute temperature and as the temperature of the gas increases, as molecules move with larger speeds and thus viscosity increases.