Metals form basic hydroxides. Which of the following metal hydroxide is the least basic?

Options

A. `Mg(OH)_(2)`
B. `Ca(OH)_(2)`
C. `Sr(OH)_(2)`
D. `Ba(OH)_(2)`

Answer

A

Explanation

All the alkaline earth metals form hydroxides. Solubility of hydroxides of alkaline earth metals increases from Be to `Ba. Be(OH)_(2)` and `Mg(OH)_(2)` are almost insoluble. The basic nature of hydroxides of alkaline earth metal depends on the solubility of hydroxide in water. more the solubility more the basicity. Solubility of hydroxides depends on lattice energy and hydration energy.
`DeltaH_("solution") = DeltaH_("lattice energy") +DeltaH_("hydration energy")`
The magnitude of hydration energy remains almost same whereas lattice energy decreases down the group leading to more negative values for `DeltaH_("solution")` down the group. More negative `DeltaH_("solution")` more is solubility of compounds. Hence, `Be(OH)_(2)` and `Mg(OH)_(2)` have less negative values for `DeltaH_("solution")` hence, least basic.