An open flask contains air at $27^{\large\circ}C$. Calculate temperature at which it should be heated so that , $\large\frac{1}{3}rd$ of air measured at $27^{\large\circ}C$ escapes out.

Question

$(a)\;177^{\large\circ}C\qquad(b)\;108^{\large\circ}C\qquad(c)\;140^{\large\circ}C\qquad(d)\;150^{\large\circ}C$

Comments

Why didn't we considered the initial volume to be x ??
Why did you used the number of moles here??