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

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: $Cr = 24, Mn = 25, Fe = 26, Co = 27$)

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

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 $W(VI)$

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

Oxygen is absorbed by molten $Ag$,which is evolved on cooling and the silver particles are scattered,this phenomenon is known as