Across a period from left to right, atomic radius generally: MCQ with Answer and Explanation

Explanation:
Global warming is the long-term rise in Earth's average temperature, primarily caused by the increased concentration of greenhouse gases (like CO₂, CH₄, N₂O) in the atmosphere. These gases trap outgoing infrared radiation, enhancing the natural greenhouse effect and leading to climate change.

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:
In 2Na + Cl₂ → 2NaCl, sodium is oxidized (Na → Na⁺ + e⁻) and chlorine is reduced (Cl₂ + 2e⁻ → 2Cl⁻). It involves change in oxidation states. Options A and B are double displacement (no change in oxidation states). Option D is decomposition with no change in oxidation states (Ca: +2 remains +2). Redox reactions involve simultaneous oxidation and reduction.