In the wet tests for identification of various cations by precipitation, which transition element cation doesn't belong to group IV in qualitative inorganic analysis?

During the qualitative analysis of $$\mathrm{SO}_{3}^{2-}$$ using dilute $$\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{2}$$ gas is evolved which turns $$\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$$ solution (acidified with dilute $$\mathrm{H}_{2} \mathrm{SO}_{4}$$) :

An indicator 'X' is used for studying the effect of variation in concentration of iodide on the rate of reaction of iodide ion with $$\mathrm{H_2O_2}$$ at room temp. The indicator 'X' forms blue coloured complex with compound 'A' present in the solution. The indicator 'X' and compound 'A' respectively are

Which one amongst the following are good oxidizing agents?

A. Sm$$^{2+}$$

B. Ce$$^{2+}$$

C. Ce$$^{4+}$$

D. Tb$$^{4+}$$

Choose the most appropriate answer from the options given below :