The standard reduction potential values of some of the p-block ions are given below. Predict the one with the strongest oxidising capacity.

An oxidising agent gets reduced itself. Hence the easier it is to get reduced, the stronger is its oxidising power.

The ease of reduction is measured by the standard reduction potential $$E^{\ominus}$$.
Larger (more positive) $$E^{\ominus}$$ ⇒ easier reduction ⇒ stronger oxidising capacity.

The given standard reduction potentials are

$$Pb^{4+} + 2e^- \rightarrow Pb^{2+},\; E^{\ominus}=+1.67\text{ V}$$

$$Sn^{4+} + 2e^- \rightarrow Sn^{2+},\; E^{\ominus}=+1.15\text{ V}$$

$$Al^{3+} + 3e^- \rightarrow Al,\; E^{\ominus}=-1.66\text{ V}$$

$$Tl^{3+}/Tl$$ (given), $$E^{\ominus}=+0.26\text{ V}$$ (value supplied in the option)

Comparing the numerical values:

$$+1.67\text{ V} \gt +1.15\text{ V} \gt +0.26\text{ V} \gt -1.66\text{ V}$$

Therefore $$Pb^{4+}$$ (Option A) has the highest positive standard reduction potential and is the most readily reduced species. Hence it possesses the strongest oxidising capacity.

Final answer: Option A