From the equation :$N_2+3H_22NH_3$ calculate the volume of ammonia gas formed when 6 litres of hydrogen reacts with excess of nitrogen , all volumes being measured at $STP$

Question

$\begin{array}{1 1} (a)\;4\;litre \\ (b)\;5\;litre \\ (c)\;6\;litre \\(d)\;8\;litre\end{array}$