Question

Which of the following metals can displace hydrogen from cold water?

• A. $\mathrm{Ca}$
• B. $\mathrm{Au}$
• C. $\mathrm{Sb}$
• D. $\mathrm{Sn}$

Answer 1

The correct option is A

$\mathrm{Ca}$

Explanation:

Reactivity series: Reactivity series is the arrangement of metal in a tabular form in the decreasing order of their reactivity.

Reactivity series:

$\mathrm{K}>\mathrm{Na}>\mathrm{Li}>\mathrm{Ba}>\mathrm{Sr}>\mathrm{Ca}>\mathrm{Mg}>\mathrm{Al}>\mathrm{Mn}>\mathrm{Zn}>\mathrm{Cr}>\mathrm{Fe}>\mathrm{Cd}>\mathrm{Co}>\mathrm{Ni}>\mathrm{Sn}>\mathrm{Pb}>\mathrm{H}>\mathrm{Sb}>\mathrm{Bi}>\mathrm{Cu}>\mathrm{Hg}>\mathrm{Ag}>\mathrm{Au}>\mathrm{Pt}$

• The metal present at a higher position can displace the element which is present below that element in the activity series.
• Since only calcium is present above hydrogen in the reactivity series among the given options.
• So, Calcium displaces hydrogen from water and forms calcium hydroxide along with the evolution of hydrogen gas.
• The balanced chemical reaction can be represented as:

$\mathrm{Ca}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Calcium Water(cold) Calcium hydroxide Hydrogen

Thus, the correct answer is Option A.