2022 H2 Chem P1 Q6 — Periodic table Solution

The answer is B (16).

Electronegativity decreases down a group and increases across a period.
• X is adjacent to arsenic in Group 15 and is more electronegative (2.1 against 2.0), so X is above arsenic: X is phosphorus (proton number 15).
• Y is adjacent to phosphorus in Period 3 and is more electronegative (2.5 against 2.1), so Y is to the right of phosphorus: Y is sulfur, proton number 16.

• A is wrong: 14 is silicon, to the left of phosphorus, which is less electronegative than phosphorus, not more.
• C is wrong: 50 is tin. It would only be a neighbour of X if X were antimony, below arsenic, but antimony is less electronegative than arsenic, while X is more electronegative. Tin is also to the left of antimony, so less electronegative than it.
• D is wrong: 52 is tellurium, the neighbour of antimony. X cannot be antimony, because X is more electronegative than arsenic.