# An open vessel containing 3 moles of an ideal gas at $300 ^{\circ}$ is heated to $500 ^{\circ}$. What is the number of moles left after heating?

(A) 1.8 (B) 3 (C) 5 (D) 2.2

For an open vessel nT = constant.
Therefore, $n_1 T_1 = n_2 T_2 \rightarrow 3 \times (300 + 273) = n_2 \times (500 + 273)$
$\Rightarrow n_2 = \large\frac{3\times 573}{773}$$\approx 2.2$