Question

what do you mean by first ionisation energy and second ionisation enegy ?

Answer 1

Second ionisation energy :
It is theenergy needed to remove asecond electron from each ion in 1 mole of gaseous 1+ ions to give gaseous 2+ ions. You canthen have as many successiveionisation energies as there areelectrons in the original atom.
First ionisation energy :
The first ionisation energy is the energy required to remove one mole of the most loosely held electrons from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+.

Answer 2

second ionisation energy is defined by the eq..it is the energy needed to remove a second electron from from each ion in 1 mole of gaseous 1+ion to give gaseous 2+ions.