The first ionisation potential of Na is 5.1 eV. The value of electron gain enthalpy of Na + will be :

Step-by-step solution

Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron. Na ( g )        →    Na + ( g ) + e − ; 1 s t ionisation energy ; ΔH I   E ( 1 ) = + 5 .1 eV Electron gaining is the reversed reaction of ionization. Hence, electron gain enthalpy is ; IE Na   =