Solution

Inert pair effect is the tendency of the 2 electrons in the outermost atomic s orbitals to remain unionized/unshared in compounds of post-transition metals. Inert pair effect says that the $${ns}^{2}$$ valence electron of metallic elements, especially the $${5s}^{2}$$ and $${6s}^{2}$$ pairs that follow the 2nd and 3rd row of transition metals, are less reactive than would be expected. Out of all the elements mentioned only Carbon does not fit into the criteria since E.C of carbon=$${1s}^{2}$$ $${2s}^{2}$$ $${2p}{2}$$ $$5s$$ and $$6s$$ orbitals are not involved in carbon