Q4. Sulphur is +4 in SO2. Can SO2 act as an oxidising agent, a reducing agent, or both?
Both. Sulphur’s states run from −2 to +6, so from +4 it can be oxidised, to +6 as in SO3 or sulphate, and it can be reduced, to 0 or −2 (states from Wikipedia, “Chalcogen”; reasoned).
Q5. Assertion: the electron gain enthalpy of oxygen is less negative than that of sulphur. Reason: oxygen is more electronegative than sulphur. Are both true, and does the reason explain the assertion?
Both are true, but the reason does not explain the assertion. The real cause is the strong repulsion an added electron meets in oxygen’s small 2p shell (NCERT Class 11 Chemistry, page 90).
Q6. Why does sulphur form S8 rings and long chains, while oxygen forms O2 molecules?
Sulphur–sulphur double bonds are far weaker than O=O, but S–S single bonds are stronger than O–O single bonds (Wikipedia, “Chalcogen”): 213 against 138 kJ mol−1 (NCERT Class 11 Chemistry, Table 5.3(a), page 154). So oxygen pairs up with a double bond, while sulphur links to itself with single bonds: it catenates (Wikipedia, “Sulfur”).
Q7. Find the percentage of fluorine by mass in SF6. (S = 32.06, F = 19.00 g mol−1.)
M(SF6) = 32.06 + 6 × 19.00 = 146.06 g mol−1. % F = 114.00/146.06 × 100 ≈ 78.05% (reasoned; percentage composition).
Q8. Hydrogen telluride decomposes above 0 °C, while water can be made by heating hydrogen and oxygen together. What trend does this show?
The thermal stability of the hydrides H2X falls down the group (Wikipedia, “Hydrogen chalcogenide”). The H–X bond weakens as X grows larger (reasoned), which also makes the heavier hydrides stronger acids (NCERT Class 11 Chemistry, Section 6.11.7, page 200).