Which of the following hydrides of Group $16$ elements has the highest reducing property?

$A$ pale yellow solid molecule $(A)$ having crown shape is heated with conc. $H_2SO_4$. It gives a suffocating smell of gas $(B)$,which when passed through starch iodate paper,turns it blue. The gas $(B)$ is:

Which of the following has an $S-S$ bond?

An amorphous solid $'A'$ burns in air to form a gas $'B'$ which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous $KMnO_4$ solution and reduces $Fe^{3+}$ to $Fe^{2+}$. Identify the solid $'A'$ and the gas $'B'$ and write the reactions involved.

How is ozone formed from the oxygen present in the atmosphere?

What are the values of electron gain enthalpy in groups $16$ and $17$? How do they change?