# S1: Heat absorbed during isothermal expansion of ideal gas in vacuum is zero.  S2: Volume occupied by molecules of ideal gas is zero.

$\begin {array} {1 1} (A)\;\text{If both S1 & S2 are correct and S2 is correct explanation of S1.} \\ (B)\;\text{If both S2 & S1 are correct but S2 is not correct explanation of S1.} \\ (C)\;\text{If S1 is correct but S2 is wrong.} \\ (D)\; \text{If S1 is wrong but S2 is correct.} \end {array}$

S1 is correct because, during isothermal expansion, there is no exchange of heat between the gas and surroundings
Ans : (B)