(i) Most reactive non metal is B

REASON: It has the highest negative electron gain enthalpy.

(ii) Most reactive metal =A

REASON: It has the lowest negative electron gain enthalpy as well as lowest first ionisation energy.

(iii) Least reactive element=D

REASON:D is the least reactive element as it has an extremely high first and second ionisation enthalpy.

(iv) Metal forming binary halide=C

REASON: it has low first ionisation enthalpy than second but the different is not much.