The first ionization enthalpies of four consecutive elements of the third period are 496 , 577 , 737 and 786 kJ mol ⁻¹ . Which of the following is the first ionization enthalpy ( kJ mol ⁻¹ ) of the element that possesses the highest second ionization enthalpy among these four?

Step-by-step solution

The given first ionization enthalpies belong to four consecutive elements of the third period: Na , Mg , Al , and Si . The general trend is an increase in ionization enthalpy across a period, but Mg ( Group 2 , 3 s ^2 ) has a higher first ionization enthalpy than Al ( Group 13 , 3 s ^2 3 p ^1 ) due to the stability of the fully-filled s-subshell. Mapping the values to the elements: Na = 496 kJ mol ⁻¹ Al = 577 kJ mol ⁻¹ Mg = 737 kJ mol ⁻¹ Si = 786 kJ mol ⁻¹ The second ionization enthalpy involves removing an electro