Solvay (ammonia soda) process is used for the manufacture of ?

The correct option is C Washing soda
Solvay (ammonia soda) process is used for the manufacture of washing soda $\left(N{a}_{2}C{O}_3\right)$.

Theory:
Sodium Carbonate $N{a}_{2}C{O}_3.10H_{2}O$

Preparation by solvay’s process:
1. Saturation of brine with $N{H}_3$ and $C{O}_2$ (in ammonia absorber)
$2N{H}_3+C{O}_2+H_{2}O⟶(N{H}_4{)}_{2}C{O}_3$
$CaC{l}_2+(N{H}_4{)}_{2}C{O}_3⟶CaC{O}_3+2N{H}_{4}Cl$
$MgC{l}_2+(N{H}_4{)}_{2}C{O}_3⟶MgC{O}_3+2N{H}_{4}Cl$

Ammoniated brine is filtered to remove Ca and Mg impurities as their insoluble carbonates.