The first ionisation enthalpies (IE) and electron gain enthalpies (EGE) of four elements P, Q, R and S are given below in kJ mol ⁻¹ : Element IE EGE P 400 -40 Q 600 -60 R 1200 -300 S 1500 -350 Which of the following pairs of elements will combine to form the compound with the highest ionic character?

Step-by-step solution

For a compound to have the highest ionic character, the electronegativity difference between the combining elements must be maximum. This condition is met when one element easily forms a cation (has the lowest ionisation enthalpy) and the other easily forms an anion (has the most negative electron gain enthalpy). From the given data, element P has the lowest ionisation enthalpy ( 400 kJ mol ⁻¹ ) and element S has the most negative electron gain enthalpy ( -350 kJ mol ⁻¹ ). Therefore, the compound formed by P and S