The question is incomplete, the complete question is shown in the image attached to this answer
Answer:
1) K
2) F
3) Si
4) Br
Explanation:
If an element has a more negative value of electron affinity, then it has a greater ability to attract an electron.
In each of the following pairs of elements, one element has a more negative electron affinity for certain reasons.
Between K and Ca, the incoming electron in K goes into a 4s orbital which is lower in energy and more stable. For Ca, the electron goes into a 3d orbital which is more unstable.
Between Ne and F, Ne already has a filled outermost shell hence the incoming electron goes into the higher energy 3s level. In F, the electron goes into the 2p level and completes it. Hence F has a more negative electron affinity.
Let us recall that half filled and completely filled orbitals are exceptionally stable. Hence, the electron affinity of Si is more negative than that of P because in P, the electron goes into an exceptionally stable half filled orbital.
Recall that the more the value of Zeff, the more negative the electron affinity hence electron affinity increases across a period; hence, Br has a more negative value of electron affinity than Se.
