Complete and balance the following chemical equations :
(i) `Al_2O_3 + Hclrarr`
(ii) `K_2O+H_2Orarr`
(iii) `Fe+H_2Orarr`
(b) An element 'X' displaces iron from the aqueous solution of iron sulphate. List v observations if the element 'X' is treated with the aqueous solutions of copper sulphate, zinc sulphate and silver nitrate. Based on the observations arrange X, Zn, Cu and Ag in increasing order of their reactivities.

Explanation

(i) `Al_2O_3 + 6HCl rarr 2AlCl_3 + 3H_2O`
(ii) `K_2O +H_2O rarr 2KOH`
(iii) `2Fe+3H_2O rarr Fe_2O_3 + 3H_2`
(b) As the element displaces iron from the solution of iron sulphate, X is higher than Fe in the reactivity series.
(i) When X is treated with aqueous solution of copper sulphate copper is displaced from the solution and blue colour of `CuSO_4` will disappear
`X + CuSO_4 rarrXSO_4 + underset("Brown")(Cu) uarr`
(ii) When X is treated with aqueous solution of zinc sulphate then Zn will be displaced if X lies higher than Zn in the activity series (K, Na, Ca, Mg, Al). If X is Zn, then nothing will happen.
(iii) If X is treated with aqueous solution of silver nitrate, then silver will be displaced and `X(NO_3)_2` will be formed.
`X + 2AgNO_3 rarr X(NO_3)_2 + underset("Silvery")(2Ag) uarr`
The metals can be arranged in increasing order of reactivity as under :
`Ag lt Cu lt Zn le X`