Valence electrons identified from successive ionization energy jumps

Steps:

• Locate sharp rises in the graph: for X, after the first IE; for Y, after the fifth IE.
• X's pattern (1 low IE then jump) indicates 1 valence electron in 3s subshell (group 1, like Na).
• Y's pattern (5 low IEs then jump) indicates 5 valence electrons in 3s²3p³ (group 15, like P).
• Group 1 loses 1 electron for Ne configuration; group 15 gains 3 electrons for octet.

Why A is correct:

• Ionization energy jumps mark valence electrons removed; X loses 1 for full shell, Y gains 3 (8 total) per octet rule.

Why the others are wrong:

• B: X (group 1) has empty 3p subshell, not five electrons.
• C: Ionization energies suggest polarity but not conclusively ionic bonding without electronegativity data.
• D: Not enough information.

Final answer: A