When $KI$ and $CuSO_4$ solutions are mixed,the products formed are:

The set of correct statements is:
$(i)$ Manganese exhibits $+7$ oxidation state in its oxide.
$(ii)$ Ruthenium and Osmium exhibit $+8$ oxidation state in their oxides.
$(iii)$ $Sc$ shows $+4$ oxidation state which is oxidizing in nature.
$(iv)$ $Cr$ shows oxidizing nature in $+6$ oxidation state.

Which statement is incorrect?

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

The number of ions from the following that have the ability to liberate hydrogen from a dilute acid is. . . . . . . .$Ti^{2+}, Cr^{2+}, V^{2+}$

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