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

Which of the following compounds does not react with cold and dil. $HNO_3$?

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

Which one of the following oxides is ionic?

Concentrated sodium hydroxide can separate a mixture of

$Cu^{2+}$ salt reacts with potassium iodide to give :