What type of oxide is $H_{2}O$?

Which metal catches fire when kept exposed to air?

Which compound is formed when dinitrogen gas reacts with dihydrogen gas?

Malachite is an ore of which metal?

Explain the following:
$(a)$ The reactivity of $Al$ decreases if it is dipped in $HNO_3$.
$(b)$ Carbon cannot reduce the oxides of $Na$ or $Mg$.

$(a)$ 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.