Plz explain it

Dear Student, Correct answer is B). It is because it is always endothermic to let an anion accept electron. In A), C) and D), one electron is being accepted by O, Cl and S which is exothermic. In B) the electron is to be accepted by an anion (O-) which is difficult on its own and requires energy to be supplied and hence the reaction absorbs energy. Regards