Which metal is used in the thermite process for welding railway tracks? MCQ with Answer and Explanation

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.

Explanation:
Catalytic poisoning occurs when a substance (a catalytic poison) binds strongly to the active sites of a catalyst, blocking reactants from adsorbing and thereby destroying or reducing its catalytic activity. Arsenic acts as a poison for the iron catalyst used in the Haber process for ammonia synthesis.

Explanation:
Soap solution is basic, pH > 8.3, so it turns phenolphthalein pink. Lemon juice (citric acid) and vinegar (acetic acid) are acidic, pH < 7, phenolphthalein remains colorless. Hydrochloric acid is strongly acidic, colorless. Phenolphthalein indicator is colorless in acidic and neutral, pink in alkaline solutions. It is used in titrations.