Of the three metals $X, Y$ and $Z$,$X$ reacts with cold water,$Y$ with hot water,and $Z$ with steam only. Identify $X, Y$ and $Z$ and also arrange them in the order of increasing reactivity.

(A) $X$ is an alkali metal,such as $Na$ or $K$,which is highly reactive and reacts with cold water.
$Y$ is an alkaline earth metal,such as $Mg$ or $Ca$,which reacts with hot water.
$Z$ is a metal like $Fe$ (iron),which reacts only with steam.
The order of increasing reactivity is $Z < Y < X$,which corresponds to $Fe < Mg < Na$.