Assertion: In an isochoric process $p-V$ graph is straight line parallel to $p$ -axis.

Reason: In an isochoric process density $\mathrm{\rho }$ remains constant.

Assertion For given source and sink temperatures efficiency of Carnot's engine is $100\%$.

Reason For given source and sink temperatures efficiency of Carnot's engine is maximum.

Assertion: Efficiency of any heat engine cannot be greater than the heat engine of Carnot's engine.

Reason: Heat flow never takes place from a body at lower temperature to a body at higher temperature.

Assertion: If the volume of a gas is increasing but the temperature of the gas is decreasing, then the heat given to the gas may be positive, negative or zero.

Reason: Heat given to a gas is a state function. It is not path function.

Assertion: First law of thermodynamics can be applied only for an ideal or real gas system.

Reason: First law of thermodynamics is nothing but law of conservation of energy.

Assertion: There are two processes : Process 1 is $pV=$ constant and process $2$ is $p{V}^2=$ constant. In both the processes volume of gas is increased from $V_1$ to $V_2$. Initial coordinates $\left(p_1\text{,} V_1\right)$ of the gas were the same. Then, more work is done by the gas in process $1$.

Reason: In second process pressure drops more rapidly with increase in volume.

Assertion: Any process taking place in the atmosphere is considered as an isobaric process.

Reason: Work done by the system in that case is $p_0\mathrm{\Delta }V$. Where, $p_0$ is atmospheric pressure.

Assertion: During melting of ice work done by surrounding on (ice + water) system is positive.

Reason: Volume of the given system decreases on melting of ice.

Assertion: Molar heat capacity cannot be defined for an isothermal process.

Reason: In isothermal process $\left(pV\right)$ versus $T$ graph is a dot.