Assertion (A): Ethene decolorizes bromine water. Reason (R): Ethene undergoes an addition reaction with bromine. MCQ with Answer and Explanation

Explanation:
Across a period, electrons are added to the same shell, but the number of protons increases, leading to a greater effective nuclear charge. This pulls electrons closer, decreasing atomic radius and making it harder to remove an electron, so ionization energy increases.

Explanation:
Autocatalysis occurs when one of the products of a chemical reaction acts as a catalyst for that same reaction. As the reaction proceeds and the product accumulates, the rate of the reaction increases. A classic example is the oxidation of oxalic acid by potassium permanganate, where the Mn2+ ions produced catalyze the reaction.

Explanation:
Evaporation of water is a physical change—liquid water changes to water vapor, but the chemical composition (H₂O) remains unchanged. Souring of milk and curd formation involve lactic acid bacteria converting lactose to lactic acid (chemical change). Fermentation of grapes involves yeast converting sugars to ethanol and CO₂. Chemical changes produce new substances. Physical changes only alter the state or form.