In a redox reaction: MCQ with Answer and Explanation

Explanation:
Atomic radius decreases across a period because the effective nuclear charge increases while electrons are added to the same shell, pulling the electron cloud closer. Down a group, radius increases due to addition of new shells.

Explanation:
Ionic compounds consist of positive and negative ions held together by strong electrostatic forces of attraction (ionic bonds). A large amount of energy is required to overcome these forces, resulting in high melting and boiling points. They also conduct electricity when molten or in solution.

Explanation:
Rusting is an electrochemical process requiring both oxygen and water (moisture). The overall reaction: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O. In the absence of either, rusting does not occur. Salt accelerates rusting by increasing conductivity. Prevention methods include painting, greasing, galvanization, and cathodic protection. Rust is hydrated iron(III) oxide, a reddish-brown flaky substance, not protective.