Correct Option: B

The first ionisation energy is the energy required to remove the most loosely held electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+. The first first ionisation energy (in KJ per mole) of Hydrogen: around 1200; Helium: about 2500; Lithium: about 500; and Sodium: about 500.