(a) Be2 :
Beryllium has an atomic number of 4.
Electronic configuration: 1s2, 2s2.
Be2 is a gas and its orbitals are fully occupied and hence will have very low/nil electron affinity.
Fluorine has an atomic number of 9.
Electronic configuration: 1s2, 2s2, 2p5
Here two atoms of fluorine have bonded together and will have low electron affinity (vacancy of 2 electrons in 2 atoms).
Atomic number of boron = 5
electronic configuration: 1s2, 2s2, 2p1.
and here the boron atoms have lost the p-orbital electron, and so have less affinity for electrons.
Carbon has an atomic number of 6
electronic configuration: 1s2, 2s2, 2p2
In the given scenario, (d) will have the highest affinity for electrons, since its p-orbital is mostly unfilled.