Which of the following does not react with oxygen directly? $Zn$,$Ti$,$Pt$,$Fe$

Iron may be rendered passive by treatment with a concentrated solution of

Transition metal with low oxidation number will act as

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

Which of the following are basic oxides among $Mn_2O_7 (I)$,$V_2O_3 (II)$,$V_2O_5 (III)$,$CrO (IV)$,and $Cr_2O_3 (V)$?

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