Question

Which of the followings readily react with cold water?

Answer 1

Berylium is kinetically inert toward water even when they are red hot. This is due to the formation of protective layer around them. Its an oxide layer which is stable even at higher temperature and protects the metal.

Mg also inert toward cold water due to the protective oxide layer but they are decomposed by hot water since the protective layer is not stable at high temperature.
$Mg+2H_{2}O\to Mg(OH{)}_2+H_2$

Ba and Ca are readily react with cold water because they didn't form any protective oxide layer.

$Ca+2H_{2}O\to Ca(OH{)}_2+H_2$
$Ba+2H_{2}O\to Ba(OH{)}_2+H_2$
Hence, the correct options are a.