Manganese dioxide on heating with concentrated hydrochloric acid gives a greenish yellow gas,$X$. With excess of ammonia,$X$ gives $Y$ and $Z$. $Y$ and $Z$ respectively are:

• A
  $NH_4F, N_2$
• B
  $NH_4I, NOCl$
• C
  $NCl_3, HOCl$
• D
  $NH_4Cl, N_2$