What happens when
(a) Calcium reacts with water
(b) Iron reacts with steam
(c ) Magnesium reacts with hot water
(d) Sodium reacts with water
Arrange the above metals in order of decreasing activity.

Explanation

(a) calcium reacts with water to form calcium hydroxide and hydrogen gas.
`undersetunderset("metal")("Calcium")(Ca_((s)))+underset("water")(2H_(2)O_((l)))tounderset("Calcium hydroxide")(Ca(OH)_(2(aq.)))+underset("Hydrogen")(H_(2(g)))`
(b) Iron reacts with steam to form iron (II,III) oxide and hydrogen.
`3Fe_((s)) + 4H_(2)O_((g)) to underset("Iron (II,III) oxide") (Fe_(3)O_(4(s))) + 4H_(2(g))`
(c ) Magnesium reacts with hot water to form magnesium hydroxide and hydrogen.
`Mg_((s)) + 2H_(2)O_((l)) to undersetunderset("Magnesium hydroxide")(Mg(OH)_(2(aq.))) (H_(2(g))`
Sodium reacts with water to form sodium hydroxide and hydrogen gas. the reaction is so violent that the evolved hydrogen immediately catches fire.
`Na_((s)) +H_(2)O_((l)) to NaOH_((aq)) + 1//2H_(2(g))`
The arrangement of metals in decreasing order of activity is : `Na gt Ca Mg gt Fe`