Consider the following two statements.
A. If heat is added to a system, its temperature must increase.
B. If positive work in done by a system in a thermodynamic process, its volume must increase.
Statement A: For an isothermal process (where the temperature remains constant) if heat is added to a system temperature will not increases. So, statement A is wrong.
Statement B: We know that,
Work done = force ×displacement
Volume = area ×displacement
Therefore,
Work done=pressure ×volume
Let change in the volume of system = ΔV = V2-V1
Pressure =P
Thus, work done by the system W at constant pressure
W=PΔV
W>0 and positive only when V2 > V1.
Therefore, statement B is correct.