Which of the following reactions is NOT a redox reaction? MCQ with Answer and Explanation

Explanation:
Soap (sodium/potassium salts of long-chain fatty acids) reacts with Ca²⁺ and Mg²⁺ ions in hard water to form insoluble calcium/magnesium salts (scum), which precipitates and does not lather. This wastes soap. Reaction: 2RCOONa + Ca²⁺ → (RCOO)₂Ca↓ + 2Na⁺. Detergents do not form scum because their calcium salts are soluble. Hardness is measured in ppm of CaCO₃.

Explanation:
Camphor sublimes—it directly changes from solid to vapor on heating without passing through the liquid phase. Other sublimable solids include naphthalene, iodine, ammonium chloride, and dry ice (solid CO₂). Sodium chloride, sugar, and sand melt or decompose on strong heating. Sublimation is used to separate sublimable substances from non-sublimable impurities. The process requires careful heating.

Explanation:
J.J. Thomson proposed the 'Plum Pudding' model in 1904 after discovering the electron. He envisioned the atom as a sphere of positive charge with negatively charged electrons embedded within it, like plums in a pudding. This was later disproved by Rutherford's gold foil experiment.