Question

Assertion $\left(A\right)$ : At critical temperature liquid passes into gaseous state imperceptibly and continuously.

Reason $\left(R\right)$: The density of liquid and gaseous phase is equal at critical temperature.

• A. $A$ is false but $R$ is true.
• B. Both $A$ and $R$ are true, but $R$ is not the correct explanation of $A$.
• C. Both $A$ and $R$ are true, and $R$ is the correct explanation of $A$.
• D. $A$ is true but $R$ is false.

Answer 1

The correct option is C Both $A$ and $R$ are true, and $R$ is the correct explanation of $A$.

Analysing the assertion & reason

At critical temperature, it is not possible to state whether the substance is in the gaseous form or in the liquid form. In fact, both the states become indistinguishable at the critical point. The surface of separation between liquid and gas disappears. At this point, the various physical properties such as density, refractive index etc., have identical values for the states. So, at critical temperature, the liquid changes into gaseous state imperceptibly and continuously.
So, both assertion and reason are correct, and reason is the correct explanation of the assertion.
Hence, option $\left(A\right)$ is the correct answer.