c
Generally, the ionization enthalpies or energy increases from left to right in a period and decreases from top to bottom in a group. Several factor such as atomic radius, nuclear charge, shielding effect are responsible for change of ionization enthalpies Here, \(1^{st}\) ionization enthalpy of \(A\) and \(B\) is greater than group \(I\) (\(Li\, 520\, kJ\,mol^{-1}\) to \(Cs\,374\, kJ\,mol^{-1}\)), which means element \(A\) and \(B\) belong to group \(-2\) and all three given ionization enthalpy values are less for element \(B\) means \(B\) will come below \(A\).