Which of the following oxidation state is common for all lanthanoids?

Which of the following reactions are disproportionation reactions?

(i) $\mathrm{Cu}^{+} \longrightarrow \mathrm{Cu}^{2+}+\mathrm{Cu}$

(ii) $3 \mathrm{MnO}_4^{-}+4 \mathrm{H}^{+} \longrightarrow 2 \mathrm{MnO}_4^{-}+\mathrm{MnO}_2+2 \mathrm{H}_2 \mathrm{O}$

(iii) $2 \mathrm{KMnO}_4 \longrightarrow \mathrm{~K}_2 \mathrm{MnO}_4+\mathrm{MnO}_2+\mathrm{O}_2$

(iv) $2 \mathrm{MnO}_4^{-}+3 \mathrm{Mn}^{2+}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow 5 \mathrm{MnO}_2+4 \mathrm{H}^{+}$

When $\mathrm{KMnO}_4$ solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because

There are 14 elements in actinoid series. Which of the following elements does not belong to this series?

$\mathrm{KMnO}_4$ acts as an oxidising agent in acidic medium. The number of moles of $\mathrm{KMnO}_4$ that will be needed to react with one mole of sulphide ions in acidic solution is