An element occupies group No.16 and period number 2. This element
on passing through silence electric discharge forms (A). (A) also reacts
with lead sulphide and forms (B). (A) also reacts with BaO 2 and forms
(C). It reacts with H 2 O 2 and forms (D). Identify the dement (A), (B),
(C) and (D).