The incorrect statement among the following is :-

Which of the following are used as catalysts in petroleum cracking?

The transition element of $III-B$ group which forms an alum isomorphic with $Al_2(SO_4)_3 \cdot 18H_2O$ is $Sc$. The color of the compound $Sc_2(SO_4)_3 \cdot (NH_4)_2SO_4 \cdot 24H_2O$ is:

The color of $KMnO_4$ is due to:

Fill in the blanks:
$(1)$ In the dichromate ion,the $O-Cr-O$ bond angle is ....... $^o$.
$(2)$ The reaction $3Sn^{2+} \to 3Sn^{4+} + 6e^-$ occurs via .........,in which $Sn^{2+}$ is ......... .
$(3)$ The symbols for stannous and stannic are ......... and ......... respectively.
$(4)$ $V_2O_4$ dissolves in acidic compounds to give ......... salts.

Provide the structures for:
$1.$ $MnO_4^{-}$
$2.$ $MnO_4^{2-}$