Which of the following oxidation states of manganese exhibits the most powerful oxidizing property?

Iron exhibits $+2$ and $+3$ oxidation states. Which of the following statements is incorrect for iron?

The electronic configuration of $Cu(II)$ is $3d^9$ whereas that of $Cu(I)$ is $3d^{10}$. Which of the following is correct?

When $SO_{2}$ is passed through acidified $K_{2}Cr_{2}O_{7}$ solution:

How would you account for the following:
$(i)$ Of the $d^{4}$ species,$Cr^{2+}$ is strongly reducing while $Mn^{3+}$ is strongly oxidising.
$(ii)$ $Co^{2+}$ is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.
$(iii)$ The $d^{1}$ configuration is very unstable in ions.

Which of the following characteristics of the transition metals is associated with their catalytic activity?