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Select the correct order of atomic/ionic radii:

1. K > Ca > P > Mg > N
2. Cl-(g) > S2-(g) > F-(g) > Na+(g)
3. Be2+(aq) > Li+(aq)
4. Co ≈ Ni ≈ Zn

Correct answer: K > Ca > P > Mg > N

Solution

Among the given options, option A states K > Ca > P > Mg > N. Atomic radii: K (period 4, group 1) > Ca (period 4, group 2). Then P (period 3, Z=15) vs Mg (period 3, Z=12): Mg > P in atomic radius. So the order K > Ca > Mg > P > N is correct, but the given option has P > Mg which appears wrong. However, checking all other options: B is wrong (S2- > Cl- > F- > Na+ is the correct order by iso-electronic comparison and actual values); C is wrong (Li+(aq) has larger hydration sphere than Be2+(aq) so Be2+(aq) has smaller ionic radius — actually hydrated radius of Li+ > Be2+, so Be2+(aq) < Li+(aq) in effective size); D is wrong (Zn is larger than Co and Ni due to filled d-shell). Among the choices, A is the best/only defensible answer despite the P>Mg anomaly, as the other three are clearly incorrect.

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