$(a)$ Why does calcium start floating when added to water?
$(b)$ Most metals do not release hydrogen gas when reacting with nitric acid. Why?
$(c)$ Write the chemical equation for the reaction of iron with steam. Name the compound of iron obtained.

(A) Calcium starts floating when added to water because the bubbles of hydrogen gas formed during the reaction stick to the surface of the metal,making it buoyant.
$(b)$ Nitric acid $(HNO_{3})$ is a strong oxidizing agent. When it reacts with metals,it oxidizes the hydrogen gas produced to water $(H_{2}O)$ and itself gets reduced to nitrogen oxides $(N_{2}O, NO, NO_{2})$.
$(c)$ The chemical equation is: $3Fe(s) + 4H_{2}O(g) \rightarrow Fe_{3}O_{4}(s) + 4H_{2}(g)$.
The compound obtained is iron($II$,$III$) oxide,also known as ferroferric oxide $(Fe_{3}O_{4})$.