Which of the following properties increases from left to right along the period but decreases down the group…

Analyze the question: We need properties that (a) increase from left to right across a period AND (b) decrease down a group.

Check each property:

• i. Atomic number: Increases across a period, but it also increases down a group. It fails the "decreases down the group" condition. ✗
• ii. Ionization energy: Increases across a period because the nuclear charge increases while the atomic radius decreases, so electrons are held more tightly. It decreases down a group because the atomic radius and shielding increase, so the outer electron is held less tightly. ✓
• iii. Metallic character: Decreases across a period and increases down a group. This is the opposite of what is required. ✗
• iv. Electron affinity: Generally becomes more negative (greater attraction for electrons) across a period, and generally decreases in magnitude down a group because the incoming electron is farther from the nucleus. The trend is the standard one taught for JAMB. ✓ (Noble gases and a few irregularities, like F and Cl, are exceptions, but the general trend is accepted.)

Answer: Properties ii and iv satisfy both conditions, so the answer is B. ii and iv only.

Tip: Remember that "Ionization energy, electron affinity and electronegativity" move together: they increase across a period and decrease down a group. Metallic character and atomic radius do the opposite: they decrease across a period and increase down a group. Atomic number only ever increases.