For $N{H}_{4}HS\left(s\right)\rightleftharpoons N{H}_3\left(g\right)+H_{2}S\left(g\right)$ K_P = 100 atm², equilibrium pressure equals to    

 $N{H}_{4}HS\left(s\right)\rightleftharpoons N{H}_3\left(g\right)+H_{2}S\left(g\right)$

         -                       0               0             at t = 0sec

          -                      p               p             at eq

${\mathrm{K}}_{\mathrm{c}} = \mathrm{p} \mathrm{x} \mathrm{p}$

100 = P² 

p =10 atm

P_total =10 + 10 =20 atm

 K_P = 100 atm², equilibrium pressure equals to    

Equilibrium pressure equals to 20 atm.

Hence, the correct option will be (C)