Question

The reactivity of iron, magnesium, sodium and zinc towards water are in order as:
(A) $Fe > Mg > Na > Zn$
(B) $Zn > Na > Mg > Fe$
(C) $Na > Mg > Zn > Fe$
(D) $Mg > Na > Fe > Zn$

Answer 1

The arrangement of metals in a vertical column in the order of their decreasing reactivity is called the reactivity series of metals. Here first we discuss the highly metallic nature of ion, magnesium, sodium and zinc.

Complete step by step solution:
Metals tend to lose electrons and form ions with positive charges. So in water metal loses electrons and produces hydroxide and hydrogen. Since, sodium, shows higher metallic nature than Magnesium ($Mg$), Zinc $(Zn)$ and Iron $(Fe)$, hence the reactivity order for reaction with water is
$Na > Mg > Zn > Fe$

So, the correct option is (C).

Additional Information:
Reactions of metals with water:
When a metal reacts with water, a metal hydroxide and hydrogen are formed.
For example:
Sodium reacts vigorously with water:
Sodium $+$ water $\to$ sodium hydroxide $+$ hydrogen
$2Na(s) + 2{H_2}O(l) \to 2NaOH(aq) + {H_2}(g)$
Calcium reacts readily with water:
Calcium $+$ water $\to$ Calcium hydroxide $+$ hydrogen
$Ca(s) + 2{H_2}O(l) \to Ca{(OH)_2}(g)$
Calcium hydroxide is slightly soluble in water so once the solution is saturated, it starts to become milky as solid calcium hydroxide appears.
The reactions of metals with water produce hydrogen gas $\left( {{H_2}} \right)$ and the hydroxides of the metals. Metals with moderate to low reactivity react very slowly with water. However, they react moderately with the stream when heated and give hydrogen gas and metal oxides.

Note: Beryllium $\left( {Be} \right)$ is the only alkaline earth metal that does not react with water on steam, even if the metal is heated to bed heat. Additionally, Beryllium has a resistant outer oxide layer that lowers its reactivity at lower temperatures.