Identify the correct formula of halides of alkaline earth metals from the following.

1.  ${\mathrm{BaCl}}_{2}·2{\mathrm{H}}_{2}\mathrm{O}$

2.  ${\mathrm{BaCl}}_{2}·4{\mathrm{H}}_{2}\mathrm{O}$

3.  ${\mathrm{CaCl}}_{2}·6{\mathrm{H}}_{2}\mathrm{O}$

4.  ${\mathrm{SrCl}}_{2}·4{\mathrm{H}}_{2}\mathrm{O}$

Choose the correct option
1. (a, b)
2. (b, c)
3. (c, d)
4. (a, c)

Hint: Hydration energy decreases down the group

All the chlorides of alkaline earth metals are hydrated to different extents and the extent of hydration decreases from Mg to Ba e.g. ${\mathrm{MgCl}}_{2}·6{\mathrm{H}}_{2}\mathrm{O}$${\mathrm{CaCl}}_{2}·6{\mathrm{H}}_{2}\mathrm{O}$${\mathrm{BaCl}}_{2}·2{\mathrm{H}}_{2}\mathrm{O}$${\mathrm{SrCl}}_{2}·2{\mathrm{H}}_{2}\mathrm{O}$.