(a) Write the chemical reactions taking place when :
(i) Manganese dioxide is heated with aluminium powder
(ii) Steam is passed over red hot iron
(c ) Magnesium reacts with hot water.
(b) The oxide `X_(2)O_(3)` is unaffacted by water. Name a method by which metal X can be obtained from its ore. Give one reason as to why have you chosen this method.

Explanation

(i) `3MnO_(2)(s) + 4Al(s) overset("heat")rarr3Mn(s) + 2Al_(2)O_(3)(s)`
(ii) `3Fe(s) + 4H_(2)O(g) rarrunderset("Iron (II, III) oxide ")(Fe_(3)O_(4)(s) + 4H_(2)(g))`
(iii) `Mg(s) + underset(("Stream"))(2H_(2)O(g))overset("heat")rarrMg(OH)_(2)(aq)+H_(2)(g)`
(b) Since the metal oxide `X_(2)O_(3)` is not affected by water, this means that the metal is of low reactivity. It can be isolated by Alumino thermic process i.e. by reacting with metal like aluminium. For example, the metal Cr(X = Cr) can be obtained from its oxide `Cr_(2)O_(3)` by heating with aluminium.
`Cr_(2)O_(3)(s) + 2Al(s) overset("heat")rarr Al_(2)O_(3)(s) + 2Cr(s)`