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Question

(i) Arrange the following metals in an increasing order of their reactivity towards water: Zn, Fe, Mg, Na.
(ii) Arrange the following in increasing order of their oxides to get reduced with carbon: Al, Na, Fe, Cu.
(iii) Arrange the following metals in order of decreasing order of their chemical reactivity: Mg, Ca, Cu, Fe, Na, Zn, Pb.

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Solution

(i) The increasing order of the reactivity of metals towards water is
Fe < Zn < Mg < Na
As the reactivity of metals decreases from Na to Fe, their reactivity towards water decreases. Sodium reacts vigorously with cold water forming sodium hydroxide and liberates hydrogen gas. Reaction of magnesium with cold water is slow. However, with steam, red hot magnesium reacts to form an oxide and liberates hydrogen gas. Zinc does not react with cold water or steam but red hot zinc reacts with steam to form an oxide and liberates hydrogen gas. Iron also does not react with cold water or steam but red hot iron reacts reversibly with steam to form an oxide and hydrogen gas. Thus, the reactivity of metals with water decreases from sodium to iron.

(ii) The increasing order of reactivity of metal oxides to get reduced with carbon are:
Na < Al < Fe < Cu
Highly reactive metals placed at top of reactivity series, sodium and aluminium are not reduced by carbon as their affinity towards oxygen is more than carbon, thus their oxides are reduced by electrolysis process. Iron and copper (less reactive than iron) placed in the middle of reactivity series are less reactive and thus their oxides are reduced by carbon.

(iii) The decreasing order of chemical reactivity of the given metals are arranged as follows:
Na > Ca > Mg > Zn > Fe > Pb > Cu
Metals placed at the top of the activity series are highly reactive while metals placed at the bottom of the activity series are least reactive and metals placed at the middle of the reactivity series are moderately reactive.

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