Which of the following forms a set of a complex and a double salt, respectively?

• Correct answer
  A

  $\mathrm{K}_2 \mathrm{PtCl}_2 \cdot 2 \mathrm{NH}_3$ and $\mathrm{KAl}\left(\mathrm{SO}_4\right)_2 \cdot 12 \mathrm{H}_2 \mathrm{O}$
• B

  $\mathrm{NiCl}_2 \cdot 6 \mathrm{H}_2 \mathrm{O}$ and $\mathrm{NiCl}_2\left(\mathrm{H}_2 \mathrm{O}\right)_4$
• C

  $\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}$ and $\mathrm{CuCl}_2 \cdot 4 \mathrm{NH}_3$
• D

  $\mathrm{PtCl}_2 \cdot 2 \mathrm{NH}_3$ and $\mathrm{PtCl}_4 \cdot 2 \mathrm{HCl}$

Solution

$\mathrm{K}_2 \mathrm{PtCl}_2 \cdot 2 \mathrm{NH}_3$ is complex compound
$\mathrm{KAl}\left(\mathrm{SO}_4\right)_2 \cdot 12 \mathrm{H}_2 \mathrm{O}$ is empirical formula of potash alum which is a double salt $\mathrm{K}_2 \mathrm{SO}_4 \cdot \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3 \cdot 24 \mathrm{H}_2 \mathrm{O}$

Hence, the correct answer is option: 'A'.