Electron count determines periodic table group

Steps:

• Atomic number equals total electrons: W (9, fluorine), Y (19, potassium), Z (35, bromine).
• Outer shell electrons define group: W has 7 valence electrons (group 17), Z has 7 valence electrons (group 17), Y has 1 valence electron (group 1).
• W and Z share group 17, confirming same group.
• Y's properties align with alkali metal behavior.

Why A is correct:

• W and Z both have 7 valence electrons, placing them in group 17 (halogens) per periodic table grouping by valence electrons.

Why the others are wrong:

• B: No electron count for X, so cannot predict bonding with Y.
• C: No electron count for X, so cannot classify as metal.
• D: Y (19 electrons) is potassium, an alkali metal, not a non-metal.

Final answer: A