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Choose the CORRECT statement(s):

1. The smallest anion in the periodic table is H-
2. The ionic mobility of Mg2+(aq) is greater than that of Be2+(aq)
3. The electronegativity of Pb2+ is more than that of Pb4+
4. The second ionisation energy of Al is higher than the second ionisation energy of Mg

Correct answer: The ionic mobility of Mg2+(aq) is greater than that of Be2+(aq)

Solution

Be2+ has a very small ionic radius (~0.27 A) and extremely high charge density, so it is heavily hydrated in water. Its hydrated ionic radius is much larger than that of Mg2+(aq), giving it lower ionic mobility. Hence Mg2+(aq) > Be2+(aq) in ionic mobility. The other options: H- is not the smallest anion (F- in ionic form is commonly considered); higher oxidation state Pb4+ is more electronegative than Pb2+ (not less); second IE of Al requires removing from a filled 2p6 subshell which is actually easier than Mg's second IE from 3s1.

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