Assertion : oxides sulphur to acid ( S + VI) but only oxidizes selenium to ( Se + IV ).
Reason : In Selenium atoms, the electrons are more tightly held by the nucleus on account of increased nuclear charge.
(A) Filling of 10 electrons in 3d-subshell enhances the effective nuclear charge on account of the
poor sheilding and thus the electrons are held more tightly. This is the reason why selenium is
reluctant to attain the highest oxidation state of (VI).