Volume of the room is given as $V=25.0 \mathrm{~m}^{3}$

Temperature of the room is given as $T=27^{0} \mathrm{C}=300 \mathrm{~K}$

Pressure in the room will be $P=1 \mathrm{~atm}=1 \times 1.013 \times 10^{5} \mathrm{~Pa}$

The ideal gas equation can be written as:

$P V=\left(k_{B} N T\right)$

Where,

$\mathrm{K}_{\mathrm{B}}$ is Boltzmann constant having value
$\left(1.38 \times 10^{-23}\right) \mathrm{m}^{2} \mathrm{~kg} \mathrm{~s}^{-2} \mathrm{~K}^{-1}$

$\mathrm{N}$ is the number of air molecules in the room

Therefore,

$\begin{array}{l}
N=\left(P V / k_{B} T\right) \\
=\left(1.013 \times 10^{5} \times 25\right) /\left(1.38 \times 10^{-23} \times 300\right)
\end{array}$

We get,

$=6.11 \times 10^{26}$ molecules

As a result, $6.11 \times 10^{26}$ is the total number of air molecules in the given room.