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\(I.\) The radii of an anion is larger than that of the parent atom.As the parent atom is neutral and have same number of protons and neutrons. Whereas in case of its anion, the electrons are more in number than the number of protons, so effective nuclear charge of anion, is less than that of the parent atom, hence due to lesser effective nuclear charge of the anion than that of the parent chain the size of the anion is larger than that of the parent atom.

\(II.\) The ionization energy generally increases with increasing atomic number in a period.

As left to right the size decreases due to increase in the atomic number (means protons), leading to increase in effective nuclear charge hence the size decreases so the ease of releasing the electrons becomes lesser, so the ionisation energy to remove the electrons increases left to right in the same period.