Mendeleev's periodic table left a gap for an element he called eka-aluminium. This element is now known as: MCQ with Answer and Explanation

Explanation:
Smelting is the pyrometallurgical process of extracting a metal from its ore by heating it beyond its melting point and reducing the metal oxide with a carbonaceous reducing agent (like coke or coal). Flux is often added to remove impurities as slag. Calcination and roasting are oxidation processes.

Explanation:
Biogas is produced by anaerobic decomposition of organic matter (cow dung, agricultural waste) and typically contains 50-70% methane (CH₄), 30-40% CO₂, and traces of H₂S, NH₃, and H₂. Methane provides the fuel value. Biogas is a renewable fuel used for cooking and electricity generation. The slurry is good manure.

Explanation:
Bakelite, the first fully synthetic plastic, is a thermosetting phenol formaldehyde resin. It is formed by a condensation reaction between phenol and formaldehyde. Once molded and heated, it sets permanently and cannot be remelted. It is used for electrical switches, utensil handles, and jewelry.