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

(i) Since the lewis acid (X) fumes in moist air, the anion of lewis acid (X) is chloride ion.
(ii) Since the acidic solution of (X) does not give precipitate with `H_(2)S`, the cation of (X) must belong to group III of qualitative analysis i.e., `Fe^(3+),Al^(3+),Cr^(3+)` etc.
(iii) Since acidic solutino of (X) on addition of `NH_(4)Cl` and `NH_(4)OH` gives a white ppt which dissolves in NaOH solution, therefore cation of (X) must be `Al^(3+)`. thus, x= anhydrous `AlCl_(3)`.
the chemical equations for reactions at steps (i), (ii), (iii) are
(a) `AlCl_(3)+3H_(2)O to Al(OH)_(3)+ 3HCl ("fumes")`
(b) `HCl+NH_(4)OH to underset("White fumes")(NH_(4)Cl)+H_(2)O`
(c) `AlCl_(3)+3NH_(4)OH to underset(("White ppt."))(Al(OH)_(3)darr)+3NH_(4)Cl`
`Al(OH)_(3)+NaOH to underset("Sod meta aluminate (Soluble)")(NaAlO_(2))+2H_(2)O`