${\left(N{H}_4\right)}_{2}C{r}_2{O}_7$ on heating liberates a gas. The same gas will be obtained by:

On heating,  ${\left(N{H}_4\right)}_{2}C{r}_2{O}_7$ gives, nitrogen gas.
 ${\left(N{H}_4\right)}_{2}C{r}_2{O}_7\to N_2+C{r}_2{O}_3+4H_{2}O$
But whenever,  $N{H}_{4}N{O}_{2}andN{H}_{4}N{O}_3$  heated, then nitrogen and nitrogen dioxide gas liberated.
 $N{H}_{4}N{O}_2\to N_2+2H_{2}O$
 $N{H}_{4}N{O}_3\to N_{2}O+2H_{2}O$
So, the correct option is A