Pair of transition metal ions having the same number of unpaired electrons is

On charging the lead storage battery, the oxidation state of lead changes from $x_1$ to $y_1$ at the anode and from $x_2$ to $y_2$ at the cathode. The values of $x_1, y_1, x_2, y_2$ are respectively :

Aldol condensation is a popular and classical method to prepare $\alpha, \beta$-unsaturated carbonyl compounds. This reaction can be both intermolecular and intramolecular. Predict which one of the following is not a product of intramolecular aldol condensation?

Benzene is treated with oleum to produce compound $(\mathrm{X})$ which when further heated with molten sodium hydroxide followed by acidification produces compound $(\mathrm{Y})$. The compound Y is treated with zinc metal to produce compound $(Z)$. Identify the structure of compound $(Z)$ from the following option.