Which of the following transition metals is used as a catalyst?

Which of the following orders is correct?

Which of the following represents the correct order of stability for the given oxidation states?

Which of the following will give a green hydrated ion?

Given below are two statements:
Statement $I$: The number of pairs, from the following, in which both the ions are coloured in aqueous solution is $3$: $[Sc^{3+}, Ti^{3+}], [Mn^{2+}, Cr^{2+}], [Cu^{2+}, Zn^{2+}]$ and $[Ni^{2+}, Ti^{4+}]$.
Statement $II$: $Th^{4+}$ is the strongest reducing agent among $Th^{4+}, Ce^{4+}, Gd^{3+}$ and $Eu^{2+}$.
In the light of the above statements, choose the correct answer from the options given below:

Which of the following is not arranged in the correct sequence?