Question

If equal masses of oxygen and nitrogen are placed in separate containers of equal volume at the same temperature, which one of the following statements is true? (Mol wt. $N_2=28gmo{l}^{-1},O_2=32gmo{l}^{-1}$)

• A. Both flasks contain the same number of molecules.
• B. The pressure in the nitrogen flask is greater than in the oxygen flask.
• C. More molecules are present in the oxygen flask.
  
• D. Molecules in the oxygen flask are moving faster on an average than the ones in the nitrogen flask.

Answer 1

The correct option is B The pressure in the nitrogen flask is greater than in the oxygen flask.

The ideal gas equation is $PV=nRT$
Where $n=\frac{w}{M}$
w is the given mass, M is the molecular mass
$PV=\frac{wRT}{M}$

P can be inferred to be inversely proportional to molecular mass
Since the Molecular mass of $N_2$ is greater than $O_2$
Hence pressure in the nitrogen flask is higher than the oxygen flask.
Therefore option b is true.

Since the molar mass of $O_2$ is greater than that of $N_2$, hence even for the same masses of the both substances the number of moles of $N_2$ will be more than $O_2$.
Hence option a and c are incorrect.

The speed of molecules of a gas is inversely proportional to its molecular mass, hence $N_2$ will be faster than $O_2$.
So option d is incorrect