$X$ $\xrightarrow{N_2, \Delta} Y$ $\xrightarrow{H_2O} Z$ (colourless gas) $\xrightarrow{CuSO_4} T$ (blue colour)
Then,substances $Y$ and $T$ are

• A
  $Y = Mg_3N_2$ and $T = CuSO_4 \cdot 5H_2O$
• B
  $Y = Mg_3N_2$ and $T = CuSO_4 \cdot 4NH_3$
• C
  $Y = Mg(NO_3)_2$ and $T = CuO$
• D
  $Y = MgO$ and $T = CuSO_4 \cdot 4NH_3$