Question

How many of the following relation(s) is/are correct regarding the given properties?

(a) $C<N>O<F$ : First ionization enthalpy

(b) $Cl>F>Br$ : First electron affinity

(c) $O>S>Se$ : Electronegativity

(d) $Li>Be>B$ : Second ionization enthalpy

(e) $B>Be>Li$ : Covalent radii

Answer 1

a) This is true because though the first ionization enthalpy increases from left to right in the periodic table due to an increase in the effective nuclear charge. N has a higher first ionization enthalpy than O as N has a half filled 2p orbital which is a stable electronic configuration.
b) As we go down the group, the electron affinity increases but Cl has a higher electron affinity than F because due to small size of F, interelectronic repulsion is high.This option is correct.
c) This is also true because electronegativity decreases down the group, as the size of the atoms increases.
d) This is wrong as the second ionization enthalpy of B is higher than Be as for second ionization energy we need to remove an electron from the stable electronic configuration of $B^{+}\left(1s^{2}2s^2\right)$.
e) Covalent radii generally follow the same trend as atomic radii and atomic radii decreases as you go from the left to the right in a periodic table. So, this is incorrect.
So the correct options are (a), (b) and (c).