WAEC Chemistry 2025 Objective — Question 34

Question 34 of 50 from the West African Examinations Council (WAEC) Chemistry 2025 Objective paper, with the correct answer and a full explanation.

A neutral atom of neon with atomic number 10 is isoelectronic with

A. K+
B. Mg2+Correct
C. Ca2+
D. Li+

Explanation

Isoelectronic species have the same number of electrons. Neon has an atomic number of 10, meaning it has 10 electrons. Mg originally has 12 electrons but loses 2 electrons to become Mg2+, so Mg2+ has 10 electrons, making it isoelectronic with neon.

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