Question

A metal `M` readily forms water soluble `MSO_(4)` water insoluble `M(OH)_(2)` and oxide `MO` which becomes inert on heating. The hydroxide is soluble in `NaOH`. Then `M` is:
A. `Be`
B. `Mg`
C. `Ca`
D. `Sr`

Answer 1

Correct Answer - A
Given, `M` reacts to give `MSO_(4)`, which is water soluble. `M` reacts to give `M (OH)_(2)`, which is water insoluble. `M` reacts to give `MO`, which becomes inert on heating. `M(OH)_(2)` is soluble in `NaOH`, this indicates that `M` is `Be`, since only `Be`, due to its small size and high ionisation enthalpy, is amphoteric and gives `M(OH)_(2)` which dissolves in `NaOH`.
`Be(OH)_(2)+2NaOHrarrNa_(2)BeO_(2)+2H_(2)O`
other facts given are true for `Be` and not for others.