The ionization energy of sodium is $495kJmo{l}^{-1}$. How much energy is needed to convert atoms present in 2.3 mg of sodium into sodium ions ?

Ionization energy of Na = 495 kJ/mol

 No. of moles of Na in 2.3 mg

$=\frac{2.3\times 10}{23}={10}^{-4}moles$

For 1 mol, energy needed is 495 kJ

Hence, for ${10}^{-4}$ mol. energy needed is $495\times {10}^3\times {10}^{-4}J=49.5J$