The first (ΔH1) and second (ΔH2) ionisation enthalpies (in kJ mol−1) and the (ΔegH) electron gain enthalpy (in kJ mol−1) of a few elements are given below:
Elements Δ1H1 Δ1H2 ΔegH
(A) P 520 7300 -60
(B) Q 419 3051 -48
(C) R 1681 3374 -328
(D) S 1008 1846 -295
(E) T 2372 5251 +48
(F) U 738 1451 -40
The most reactive metal is :