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The correct decreasing order of first io...

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

A

a) `Be gt B gt C gt N gt F`

B

b) `N gt F gt C gt B gt Be`

C

c) F gt N gt C gt Be gt B`

D

d) `N gt F gt B gt C gt Be`

Text Solution

Verified by Experts

The correct Answer is:
C
In general, as we move from left to right in a period, the ionisation enthalpy increases with increasing atomic numbers. But the ionisation enthalpy of B is lower than that of Be. This is because the electronic configuration of `B(1s^(2)" "2s^(2)" "2p^(1))` is less stable than that of `Be(1s^(2)" "2s^(2))` which has completely filled orbitals. As a result, the 2p-electron of B is not strongly attracted by the nucleus as the 2s-electron of Be. Thus, the increasing order of frist ionisation enthalpies of elements is
`F gt N gt C gt Be gt B`
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