Which of the following changes is an example of a chemical change? MCQ with Answer and Explanation

Explanation:
Flooded rice paddies promote anaerobic decomposition of organic matter, producing methane (CH₄). It is a potent greenhouse gas. Livestock also emit methane.

Explanation:
H₂O₂ is a strong oxidizing agent that damages bacterial cell walls, membranes, and essential biomolecules through oxidation, killing microorganisms. It is used as a 3% solution for wound cleaning. The foaming action is due to catalase in tissues breaking it down, releasing O₂. It is not a reducing agent, acid, or dehydrating agent.

Explanation:
Thermosets (e.g., Bakelite) form extensive cross-links between polymer chains, making them rigid. Heating breaks bonds but degrades, not remolds. Thermoplastics are linear/branched.