Question

*Which of the following isoelectronic species has the smallest size?*

1️⃣ N³⁻
2️⃣ O²⁻
3️⃣ Al³⁻
4️⃣ All have equal size
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Answer 1

Answer:

         3️⃣ Al³⁻

Explanation:

                1️⃣ N³⁻ ⇒ 7 protons , 10 electrons

                2️⃣ O²⁻⇒  8 protons , 10 electrons

                3️⃣ Al³⁻⇒ 13 protons , 10 electrons

As the number of protons in the nucleus increases the Zeff i.e. the effective force experienced by the electrons increases and gets pulled closer to the nucleus and thus the size decreases

Since Al³⁻ has the most no of protons Al³⁻ will have the smallest size and N³⁻ will be the largest.