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

At $pH = 12$,what change occurs in $Cr_2O_7^{2-}$?

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 $W(VI)$

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

The highest Mn fluoride is $MnF_4$ whereas the highest oxide is $Mn_2O_7$,because . . . . . . .

Addition of high proportions of manganese makes steel useful in making rails of railroads,because manganese