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Identify the incorrect statement from the following:

1. The van der Waals radius of iodine is greater than its covalent radius.
2. All isoelectronic ions are found in the same period of the periodic table.
3. The first ionization energy of N is greater than that of O, whereas the second ionization energy of O is greater than that of N.
4. The electron gain enthalpy of N is nearly zero, while that of P is 74.3 kJ mol⁻¹.

Correct answer: All isoelectronic ions are found in the same period of the periodic table.

Solution

Isoelectronic ions are NOT all in the same period (e.g. N3-, O2-, F- are period 2 while Na+, Mg2+ are period 3), so statement 1 is the incorrect one. The stored choice (vdW radius > covalent radius) is actually true.

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