Question

Absolute zero is the condition at which:

• A. molecular motion ceases
• B. gas becomes liquid
• C. gas cannot be liquefied
• D. random merino of molecules occur

Answer 1

Answer: (A)

The root mean square velocity of the molecules of a gas is directly proportional to the square root of absolute temperature $(T)$ of gas, that is,
$v_{\text{rms}}=\sqrt{\frac{3RT}{M}}$
where $R$ is gas constant, and $M$ is mass.
From the above relation it is evident that if absolute temperature of the gas becomes zero $(T=0)$ then the motion of molecules will cease $\left(v_{rms}=0\right)$,
Hence according to kinetic theory absolute zero is that temperature at which the motion of all the molecules of the gas stops.
It is also clear that absolute temperature can never be negative, because $v_{\text{rms }}$ can never be negative. Thus, no temperature is possible below the absolute zero.