Explain the following:
(a) Reactivity of Al decreases if it is dipped in HNO₃
(b) Carbon cannot reduce the oxides of Na or Mg
(c) NaCl is not a conductor of electricity in the solid-state whereas it does conduct electricity in aqueous solution as well as in molten state
(d) Iron articles are galvanised.
<(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.

(a) Reactivity of Aluminium decreases if it is dipped in HNO₃ because HNO₃ is a strong oxidizing agent. Hence, a layer of aluminium oxide gets deposited because of which reactivity of aluminium gets reduced.

(b) Carbon cannot reduce the oxides of Na or Mg because these are highly reactive metals. Na and Mg have a higher affinity to oxygen than carbon. Hence, carbon fails to reduce the oxides of Na and Mg.

(c) NaCl is not a conductor of electricity in the solid state whereas it does conduct electricity in an aqueous solution as well as in molten state because NaCl is an ionic compound. In a fused state, the crystal structure of the solid compound breaks, and ions can move freely. Therefore, an aqueous solution of an ionic compound conducts electricity as there are plenty of free ions that are able to conduct electric current.

(d) Iron readily reacts with atmospheric oxygen and forms rust. To avoid rusting of iron, it is galvanized.

(e) Metals like Na, K, Ca and Mg are highly reactive metals. They can form compounds with almost every element. Due to this, they are not found in their native form in nature.