An inorganic Lewis acid `(X)` shows the following reactions :
(a) It fumes in moist air.
(b) The intensity of fumes increase when a rod dippod in `NH_(4) OH` is brought near it.
( c) To an aqueous solution of `(X)`, addition of `NH_(4)Cl` and `NH_(4)OH` gives a precipitate which dissolves in `NaOH` solution.
(d) An acidic solution of `(X)` does not give a precipitate with `H_(2) S`.
Identify `(X)` and gives chemical reactions for `(a)` to `(d)`.

Explanation

`(X)` is Lewis acid and fumes in moist air, it may be anhydrous `AlCl_(3)`.
(a) `AlCl_(3) + underset("Air") (H_(2)O) rarr Al(OH)_(3) darr + underset(("Fumes"))(3HCl)`
`AlCl_(3)` fumes in moist air due to avolution of `HCl` gas.
(b) When a rod dipped in `NH_(4)OH` is brought near it, the intensity of fumes increases due to the formation of ammonium chloride `NH_(4)Cl`.
`NH_(4)OH + HCl rarr NH_(4) Cl + H_(2) O`
( c) `AlCl_(3(aq))+ 2NH_(4)OH overset (NH_(4)Cl)rarr Al(OH)_(3)darr + 3NH_(4)Cl`
`Al(OH)_(3) +NaOH rarr underset(underset(underset("metaliminate")("Sodium"))(("Soluble")))(NaAlO_(2)) + 2H_(2)O`
An aqueous solution of `(X)` i.e `AlCl_(3)` gives a white precipitate of aluminium hydroxide `Al(OH)_(3)`, on addition of `NH_(4) Cl` and `NH_(4)OH. Al(OH)_(3)` dissolves is `NaOH` solution due to the formation of sodium metaaluminate, `NaAlO_(2)`.
(d) No precipitate is formed when `H_(2)S` is passed through acidic solution of `(X)`, i.e. `AlCl_(3)`.