Question

Assertion: Compressibility factor for hydrogen varies with pressure with positive slope at all pressures.
Reason: Even at low pressure, repulsive forces dominate for hydrogen gas.

<!--td {border: 1px solid #cccccc;}br {mso-data-placement:same-cell;}--> AIIMS 2005

• A. Both assertion and reason are true and reason is the correct explanation of assertion.
• B. Assertion is true but reason is false
• C. Both assertion and reason are false
• D. Both assertion and reason are true but reason is not the correct explanation of assertion

Answer 1

The correct option is A Both assertion and reason are true and reason is the correct explanation of assertion.

In case of hydrogen, compressibility factor (Z) increases with pressure. At $273K$, $Z>1$, which shows that it is difficult to compress the gas. In this case repulsive forces dominate.
Note: For ideal gases, $Z=1$
For real gases, $Z\ne 1$
If $Z<1$, negative deviation and the gas is more compressible than expected.
If $Z>1$, positive deviation and the gas is less compressible than expected.