$Fe$,$Co$ and $Ni$ have valuable catalytic properties in processes involving

Explain the trends in $E_{M^{3+}/M^{2+}}^{o}$ electrode potential.

Iron becomes passive by ..................... due to formation of .....................

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

Identify the statements which are not correct.
$i$. $CrO_3$ and $Mn_2O_7$ are basic oxides
$ii$. $V_2O_3$ and $V_2O_4$ are acidic oxides
$iii$. $Cr(VI)$ is more stable than $W(VI)$

Transition elements with lower oxidation states act as........