Question 3 - True/False on Wax Melting, Condensation, Compost, Baking Soda - Questions at the end of the chapter - Chapter 5 Class 7 - Changes Around Us: Physical and Chemical (Curiosit

(i) True. Solid wax cannot burn directly — it must first melt, flow up the wick, and evaporate. Only the wax vapour burns. So melting is necessary for the candle to keep burning.

(ii) False. Condensing water vapour to liquid water is a physical change — only the state changes (gas → liquid). The substance is still water (H₂O). No new substance is formed.

Corrected statement: "Collecting water vapour by condensing involves a physical change."

(iii) True. When leaves decompose into compost, bacteria and fungi break down the leaf material into entirely new substances (humus, simpler nutrients). New substances are formed, so it is a chemical change.

(iv) True. Mixing baking soda with lemon juice fizzes and produces carbon dioxide — a new substance. So it is a chemical change.

→ (i) T ; (ii) F (physical, not chemical); (iii) T ; (iv) T .