Which of the following metal hydroxide is not soluble in excess of $NH_3$ solution?

$Cu^{2+}(aq.) + X^{-}(aq.) \xrightarrow{R.T.} CuX \downarrow + X_2$
$X$ cannot be

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

Assertion $(A)$: $CuI_2$ cannot be prepared by the reaction of $Cu^{2+}_{(aq)}$ with $I^{-}_{(aq)}$.
Reason $(R)$: Aqueous $Cu^{2+}$ solution is blue in colour.
The correct answer is:

Highest oxidation state of manganese in fluoride is $+4$ $(MnF_4)$ but highest oxidation state in oxides is $+7$ $(Mn_2O_7)$ because $..........$

Which of the following orders is not correct?