$I$. $Na_2Cr_2O_7 + X \xrightarrow{\Delta} Cr_2O_3$
$II$. $Cr_2O_3 + Y \xrightarrow{\Delta} Cr$
$X$ and $Y$ are :

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

Which element can have oxidation state from $4$ to $6$?

The copper $(II)$ halide which does not exist is:

Fill in the blanks:
$(a)$ The only $Mn$ halide compound that shows an oxidation state of $+7$ is ........
$(b)$ The $E^{\ominus}_{M^{II}/M}$ value is maximum negative for ........ in the $3d$ series.
$(c)$ Between $Cr^{2+}$ and $Fe^{2+}$,the stronger reducing agent is ........

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 $W(VI)$