Complete and balance the following equations :
(i) `HgCl_(2)+KI to` (ii) `Al+Cr_(2)O_(3) to`
(iii) `CuSO_(4)+H_(2)S to` (iv) `(NH_(4))_(2)Cr_(2)O_(7)overset(Delta)(to)`

Explanation

(i) `HgCl_(2)(aq)+2KI(aq) to HgI_(2)(aq)+2KCl(aq)`
(ii) `2Al(s)+Cr_(2)O_(3)(s)overset(Delta)(to)Al_(2)O_(3)(s)+2Cr(l)`
(iii) `CuCO_(4)(aq)+H_(2)S(g) to CuS(s)+H_(2)SO_(4)(aq)`
(iv) `(NH_(4))_(2)Cr_(2)O_(7)(s)overset(Delta)(to)N_(2)(g)+4H_(2)O(g)+Cr_(2)O_(3)(s)`