Question

Figure shows the pressure P vs volume V graphs for two different gas samples at a given temperature. $M_A$ and $M_B$ are masses of two samples, $n_A$ and $n_B$ are numbers of moles. Which of the following must be correct ?

• A. $M_A>M_B$
• B. $M_A<M_B$
• C. $n_A>n_B$
• D. $n_A<n_B$

Answer 1

The correct option is D $n_A<n_B$

Both the curves are at same temp T.
For a given volume, $P_A$ < $P_B$
$\therefore P_A{V}_A<P_B{V}_B$.
$\therefore n_{A}RT<n_{B}RT$ using ideal gas equation $PV=nRT$
As both T and R are constants here we get
$\therefore n_A<n_B$
As the gases are different, their molecular weight is different. So we cannot say anything about their masses. Thus D is correct.