Which of the following pairs of oxides is amphoteric in nature?

$\underset{\text{coloured}}{P(\text{soln.})}$ $\xrightarrow{\text{Air}} \underset{\text{coloured}}{Q(\text{soln.})}$ $\xrightarrow{KOH} R \downarrow$
$(R = \text{ppt. Insoluble in both excess } NaOH \text{ and excess } NH_3 \text{ solution})$
Then $P$ contains

All $Cu(II)$ halides are known except $CuI_2$,because ....

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

For the four successive transition elements $(Cr, Mn, Fe, \text{ and } Co)$,the stability of $+2$ oxidation state will be in which of the following order?
(Atomic numbers: $Cr = 24, Mn = 25, Fe = 26, Co = 27$)

Transition metal with low oxidation number will act as