Which of the following is a Lewis acid? MCQ with Answer and Explanation

Explanation:
Compressed Natural Gas (CNG) is primarily methane (CH₄). It is stored at high pressure (200-250 bar). It is used as a vehicular fuel and for cooking. LPG is primarily propane and butane. CNG is cleaner, produces less CO₂ per unit energy, and is safer in leaks as methane is lighter than air. It has high octane rating.

Explanation:
Calcium (Ca, Z=20) has configuration 2,8,8,2. 4 shells → Period 4; 2 valence electrons → Group 2. Mg is Group 2, Period 3. Sr is Group 2, Period 5. Be is Group 2, Period 2.

Explanation:
Aluminium goes from 0 to +3 oxidation state (Al → Al³⁺ + 3e⁻), so it is oxidized. Iron goes from +3 to 0 (Fe³⁺ + 3e⁻ → Fe), reduced. This is a thermite reaction, highly exothermic, used for welding. Al is the reducing agent, Fe₂O₃ is the oxidizing agent. Oxidation is loss of electrons.