The correct decreasing order of first ionisation enthalpies of five elements of second period is

Options

A. `Be gt B gt C gt N gt F`
B. `N gt F gt C gt B gt Be`
C. `F gt N gt C gt Be gt B`
D. `N gt F gt B gt C gt Be`

Answer

C

Explanation

As we move along the period, the nuclear charge increases and size of atom decreases. Therefore, it is more difficult to remove electron from an atom. Hence the sequence of first ionisation enthalpy in decreasing order is
`F gt N gt C`
But ionisation enthalpy of boron is less as compared to beryllium because first electron in boron is to be removed from p-orbital while in beryllium, is to be removed from s-orbital. More energy is required to remove electron from s-orbital as compared to p-orbital.