Which of the following compounds produces an $oxy$-$acid$ having a basicity of $2$ upon hydrolysis?

List the important sources of sulphur.

Which of the following statements is correct?

Provide information about the elements of Group $16$.

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.

Sulphur on boiling with $NaOH$ solution forms