Identify the substrate ' $A$ ' in the following conversion.

$$ \text { A } \xrightarrow[\mathrm{H}_3 \mathrm{O}^{+}]{\mathrm{AlH}_4\left(-\mathrm{Bu}_2\right)} \text { Pent-3-enal } $$

The common name of Benzene-1,4-diol is

Which of the following is the molecular formula of halous acid of chlorine?

Calculate the enthalpy of solution of potassium chloride if its $\Delta_{\mathrm{L}} \mathrm{H}=700 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $\Delta_{\text {hyd }} H=-680 \mathrm{~kJ} \mathrm{~mol}^{-1}$