Barium reacts vigorously even with cold water while Mg reacts slowly with warm water. Mg does not react with cold water easily while Beryllium does not react even with boiling water.

The correct option is A

True

Be has a tough impenetrable oxide layer that prevents reaction with water even at high temperatures. Mg also has an oxide layer but it reacts slowly with warm water.

As we go down the group, the reactivity of the metals towards water increases. Thus Barium readily, vigorously reacts even with cold water. Alkaline earth metals react with water (under suitable conditions) and liberate hydrogen.

$Ca+2H_{2}O\to Ca(OH{)}_2+H_2$

The increasing order of the reactivity (with water )is:

$Be<Mg<Ca<Sr<Ba$