Question

The order of first electron affinity of $O$ , $S$ and $Se$ is :
A. $O > S > Se$
B. $S > Se > O$
C. $Se > O > S$
D. $S > O > Se$

Answer 1

We have to remember that the electron affinity is characterized as when an electron is added to the atom to form a negative ion, the change in energy (in kJ/mol) of a neutral atom (in the gaseous phase). In other terms, the probability of the neutral atom acquiring an electron.
The second (reverse) concept is that the energy needed to extract an electron from a single-charged gaseous negative ion is electron affinity.

Complete step by step answer:
It is possible to describe electron affinity in two similar ways. Next the energy produced by the addition of an electron to an isolated gaseous atom. The second (reverse) concept is that the energy needed to extract an electron from a single-charged gaseous negative ion is electron affinity.
It is possible to use either convention. Since the creation of positive ions is often concerned with ionisation energies, electron affinities are the negative counterpart of ions.
Due to a smaller atomic scale than sulphur, Oxygen has an unusually smaller electron affinity value (-141kJmol-1) (weaker electron-electron repulsion in 3p-subshell). It's also less than that of $Se$ , $Te$ .
$S > Se > O$ .
Therefore, the correct answer to the question is option B.

Note:
We have to remember that the chemical element with the symbol O and the atomic number 8 is oxygen. In the periodic table, it is a member of the chalcogen group, a highly reactive non-metal and an oxidising agent that easily forms oxides both with most elements and with other compounds.
We need to know that the sulphur, plentiful, tasteless and odourless, is a multivalent non-metal. Sulfur is a yellow crystalline solid in its native form. It exists in nature as the pure component or minerals of sulphide and sulphate.