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 from left to right across a period `Delta_(i) H_(1)` generally increases .Thus F has the highest `Delta_(i)H_(1)` .But as discussed in Ans. 55 above in spite of higher nuclear charge of B,`Delta_(i) H_(1)` of Be is higher than that of B. Combining these two trends , the `Delta_(i)H_(1)` of the five elements decreases in the order :
`F gt N gt C gt Be gt B` i.e., option ( c) is correct.