The ratio of number of water molecules

Question:
The ratio of number of water molecules in Mohr's salt and potash alum is $\times 10^{-1}$.

(Integer answer)

Solution:

Mohr's salt : $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Fe}\left(\mathrm{SO}_{4}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$

The number of water molecules in Mohr's salt $=6$

Potash alum : $\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2} \cdot 12 \mathrm{H}_{2} \mathrm{O}$

The number of water molecules in potash alum $=12$

So ratio of number of water molecules in Mohr's salt and potash alum $=\frac{6}{12}$

$=\frac{1}{2}$

$=0.5$

$=5 \times 10^{-1}$