At $400\, K$ temperature,the volume and pressure of a gas are $200\, mL$ and $1.5\, bar$ respectively. Calculate the volume,weight (assuming the gas is $N_2$),and the number of molecules at $STP$. $[R = 8.31 \times 10^{-2}\, L\, bar\, K^{-1}\, mol^{-1}]$.

(N/A) $1$. Using the ideal gas law $PV = nRT$,calculate the number of moles $(n)$: $n = \frac{PV}{RT} = \frac{1.5 \times 0.2}{0.0831 \times 400} = 0.009025\, mol$.
$2$. At $STP$ $(273.15\, K, 1\, bar)$,the volume of $1\, mol$ of gas is $22.7\, L$. Thus,$V_{STP} = n \times 22.7 = 0.009025 \times 22.7 = 0.2048\, L = 204.8\, mL$.
$3$. Weight of $N_2$ $(M = 28\, g/mol)$: $w = n \times M = 0.009025 \times 28 = 0.2527\, g$.
$4$. Number of molecules: $N = n \times N_A = 0.009025 \times 6.022 \times 10^{23} = 5.435 \times 10^{21}$ molecules.