# The maximum number of molecules present in :

$\begin{array}{1 1} (A)\;15L\;of\;H_2\;gas\;at\;STP \\ (B)\;5L\;of\;N_2\;gas\;at\;STP \\ (C)\;0.5g\;of\;H_2\;gas \\ (D)\;10g\;of\;O_2\;gas \end{array}$

Number of molecules in $15L$ of $H_2=\large\frac{15}{22.4}$$\times N \qquad\qquad\qquad\qquad\quad\quad\;\;\;\;\;=0.669N Number of molecules in 5L of N_2=\large\frac{5}{22.4}$$\times N$
$\qquad\qquad\qquad\qquad\quad\quad\;\;\;=0.223N$
Number of molecules in 0.5g $H_2=\large\frac{0.5}{2}$$\times N \qquad\qquad\qquad\qquad\quad\qquad\;\;=0.25N Number of molecules in 10g O_2=\large\frac{10}{32}$$\times N$
$\qquad\qquad\qquad\qquad\quad\qquad\;=0.312N$
Hence (a) is the correct answer.