Which of the following alkenes does NOT exhibit cis-trans isomerism?

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?