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# 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.

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

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

Initial temperature = 300 K
Let no. of mole at 300K = n
Let new temperature be = T K
Mole coming out at T K = $\large\frac{1}{3} n$
Mole left at T K =$n - \large\frac{1}{3}n$
$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\; = \large\frac{2}{3}n$
Under constant P and V
$n_1T_1 = n_2T_2$
$n\times300 = \large\frac{2}{3}n\times T$
T = 450 K
$= 177^{\large\circ}C$