Question

The energy required for the removal of outermost electron from an isolated unipositive gaseous ion is called:

• A. first ionisation potential
• B. second ionisation potential
• C. third ionisation potential
• D. fourth ionisation potential

Answer 1

Answer: (B)

second ionisation potential

The energy required for the removal of an outermost electron from an isolated unipositive gaseous ion is called second ionization potential. Thus when $Mg$ loses one electron, it forms $M{g}^{+}$ ion. The energy released during the process corresponds to first ionization potential.
When $M{g}^{+}$ ion loses one electron to form $M{g}^{2+}$ ion, the energy released is called second ionization potential.
$Mg\to M{g}^{+}+e^{-}\Delta H=$ first ionization energy.
$M{g}^{+}\to M{g}^{2+}+e^{-}\Delta H=$ second ionization energy.