Question

Two balloons are filled, one with pure $He$ gas and other by air. If the pressure and temperature of these balloons are same, then the number of molecules per unit volume is:

• A. more in the $He$ filled balloon.
• B. same in both the balloons.
• C. more in the air filled balloon.
• D. in the ratio of $1:4$.

Answer 1

The correct option is B same in both the balloons.

Assuming the balloons having the same volume.
As $PV=nRT,$
if $P,V$ and $T$ are same, then $n$, the number of moles present will be the same whether it is $He$ or air. Hence, number of molecules per unit volume will be same in both the balloons.