Temperature $T_{f}=27+273=300 K$

Atmospheric pressure, $P_{0}=1 \times 10^{5} P a$

$ Volume\, of\, room,$ $V_{0}=30 \mathrm{m}^{3}$

$ Difference \,in\, number\, of\, molecules,$ $N_{f}-N_{i}=?$

The number of molecules

$\Rightarrow \quad N=\frac{P V}{R T}\left(\mathrm{N}_{0}\right)$

$\begin{aligned} \therefore \quad N_{f}-N_{i} =\frac{P_{0} V_{0}}{R}\left(\frac{1}{T_{f}}-\frac{1}{T_{i}}\right) \mathrm{N}_{0} \\ =\frac{1 \times 10^{5} \times 30}{8.314} \times 6.023 \times 10^{23}\left(\frac{1}{300}-\frac{1}{290}\right) \\ =-2.5 \times 10^{25} \end{aligned}$