Elements Forming Neon-Like Ions Are in Period 3

Steps:

• Electronic configuration 2.8 matches neon (atomic number 10), a stable noble gas octet.
• Elements losing electrons to reach this configuration must add neon's 10 electrons to their core, placing them in period 3.
• Sodium (atomic number 11) loses 1 electron to form Na⁺ (2.8); magnesium (12) loses 2 for Mg²⁺ (2.8); aluminum (13) loses 3 for Al³⁺ (2.8).
• These elements share period 3 but differ in group and valence electrons lost.

Why B is correct:

• Elements in the same period have identical principal quantum shells (n=3 valence), allowing loss of group-specific valence electrons to achieve the prior noble gas (neon) configuration.

Why the others are wrong:

• A: They occupy different groups (1, 2, 13) with varying valence electrons.
• C: Noble gases possess stable configurations and do not form ions by losing electrons.
• D: Transition elements involve d-block orbitals and typically lose 1-2 electrons without reaching simple 2.8 ions.

Final answer: B