Consider the following generic reaction $2A_{2}B\left(g\right)\rightleftharpoons 2A_2\left(g\right)+B_2\left(g\right).$ Some molecules of $A_{2}B\left(g\right)$ are placed in a 1L container. As time passes several snap shots of the reaction mixture are taken as illustrated below

Number of molecules of $A_{2}B\left(g\right)$ taken initially is X, number of molecules of $A_2\left(g\right)$

present at equilibrium state is Y. (X+Y) Values is (Given: $t_1<t_2<t_3$ )

,

                           $2A_{2}B\left(g\right)\underset{ }{\rightleftharpoons }2A_2\left(g\right)+B_2\left(g\right)$

$t=t_1$                     4                           2             1

$t=t_2$                     2                           4             2

$t=t_3$                     2                           4             2

After time $t_2,$ concentration of $A_{2}B,A_z\text{\hspace{0.17em}and\hspace{0.17em}}{B}_z$ not changed. So equilibrium state reached at $t_2.$

$\therefore y=4$

Initial no. of molecules of $A_{2}B=4+2=6=x$

$\therefore x+y=10$