Mohr salt is prepared from an equimolar solution of:

• A
  $FeSO_4 \cdot 7 H_2O$ and $K_2SO_4$
• B
  $FeSO_4 \cdot 7 H_2O$ and $(NH_4)_2SO_4$
• C
  $CuSO_4 \cdot 5 H_2O$ and $K_2SO_4$
• D
  $CuSO_4 \cdot 5 H_2O$ and $(NH_4)_2SO_4$