Chemistry - Complete s-block Question with Solution | TestHub

Calcium is tarnished in air, because it is covered with a thin film of oxide.

$\mathrm{C}\mathrm{a}+{\mathrm{O}}_2\to 2\mathrm{C}\mathrm{a}\mathrm{O}$

In moist air, it is slowly tarnished, but decomposes water fairly rapidly giving hydrogen.

$\mathrm{C}\mathrm{a}+2{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}\mathrm{a}{\left(\mathrm{O}\mathrm{H}\right)}_2+{\mathrm{H}}_2$