WAEC Chemistry 2025 Objective — Question 25

Question 25 of 50 from the West African Examinations Council (WAEC) Chemistry 2025 Objective paper, with the correct answer and a full explanation.

In which of the following arrangements are the ions arranged in decreasing order of ionic size?

A. F-, Na+, Mg2+, Al3+Correct
B. Al3+, Na+, Mg2+, F-
C. Mg2+, F-, Al3+, Na+
D. Na+, F-, Mg2+, Al3+

Explanation

The ionic size decreases as the charge on the ion increases, because higher charges attract electrons more strongly, making the ions smaller. The order from largest to smallest ionic size is: F- > Na+ > Mg2+ > Al3+.

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