Correct Answer - A
Aqueous `NH_(3)` means `NH_(3) + H_(2)O rarr NH_(4)OH`
`Fe^(3+) + 3OH^(Theta)` (from `NH_(4)OH) rarr Fe(OH)_(3)`
`NH_(4)OH rarr NH_(4)^(o+) + overset(Theta)OH`
Due to common ion `(NH_(4))`, the supression of ionisation of `NH_(4)OH` takes place, so the concentartion, of `overset(Theta)OH` is less. So only the `Fe(OH)_(3)` ppt. not `Mg(OH)_(2)` since `K_(sp)` of `Fe(OH)_(3) lt K_(sp) "of" Mg(OH)_(2)`
