a) As, acidic property increases with increasing oxidation number. Therefore, statement is true. b) since Cl(−) is more negative and it will have more electron gain enthalpy. Therefore, statement is wrong. c) If an element accept the electron the electron size increases and when element donate the electron the ionic size reduces. Therefore, the given order is correct. d) The K+ ion has noble gas configuration and d shell is absent, on the other hand Cu+ has fulfilled d shell i.e. d10.Therefore, the second ionisation enthalpy of K+ is more the Cu+