The catalytic activity of transition metals and their compounds is ascribed mainly to

The set of correct statements is:
$(i)$ Manganese exhibits $+7$ oxidation state in its oxide.
$(ii)$ Ruthenium and Osmium exhibit $+8$ oxidation state in their oxides.
$(iii)$ $Sc$ shows $+4$ oxidation state which is oxidizing in nature.
$(iv)$ $Cr$ shows oxidizing nature in $+6$ oxidation state.

The correct order of oxidizing power of the given ions is

For $Cr, Mn, Fe,$ and $Co$,the $E^{0}_{M^{3+}/M^{2+}}$ values are $-0.41, +1.57, +0.77,$ and $+1.97 \ V$ respectively. For which metal is the change in oxidation state from $+2$ to $+3$ the easiest?

Match the formulas given in Column-$I$ with the type of oxide given in Column-$II$ and select the correct option:-

Column-$I$	Column-$II$
$A$. $Pb_3O_4$	$I$. Neutral oxide
$B$. $N_2O$	$II$. Acidic oxide
$C$. $Mn_2O_7$	$III$. Basic oxide
$D$. $Bi_2O_3$	$IV$. Mixed oxide

The addition of dilute $NaOH$ to $Cr^{3+}$ salt solution will give: