According to the Mulliken scale, electronegativity is proportional to the average of ionisation enthalpy and electron gain enthalpy (magnitude). Element X has $I E = 1140$ and $∣ Δ_{e g} H ∣ = 330$ kJ/mol; element Y has $I E = 900$ and $∣ Δ_{e g} H ∣ = 120$ kJ/mol. The ratio $χ_{X} / χ_{Y}$ is

Answer: A

The Mulliken value is

(I E + E A) /2

, giving 735 kJ/mol for X and 510 kJ/mol for Y. The ratio is

735/510 = 1.44

. The value 1.27 comes from using only the ionisation enthalpies (1140/900) and 0.69 is the inverted ratio.