The group number for main-group elements indicates the number of valence electrons, and the common valency is often determined by how many electrons must be gained to reach a noble-gas configuration. An element in Group 16 has six valence electrons, with the configuration ns^2 np^4. To complete its octet it tends to gain two electrons, giving a common valency of two. For period 3, this element is sulphur with configuration 3s^2 3p^4, which indeed shows a characteristic valency of two as in hydrogen sulphide. The option of four valence electrons describes Group 14. The option of two valence electrons describes Group 2. The option of seven valence electrons describes Group 17. Linking group number to valence electrons and valency is a fundamental NCERT classification skill. Plausibility check: sulphur readily forms compounds such as H_2S and metal sulphides with valency two, confirming six valence electrons and a valency of two.