What is the starting material for the preparation of $KMnO_4$?

Name the oxometal anions of the first series of the transition metals in which the metal exhibits the oxidation state equal to its group number.

$A$ first row transition metal with the highest enthalpy of atomization,upon reaction with oxygen at high temperature,forms oxides of the formula $M_2O_n$ (where $n=3, 4, 5$). The 'spin-only' magnetic moment value of the amphoteric oxide from the above oxides is $......$ $BM$ (nearest integer). (Given atomic number: $Sc: 21, Ti: 22, V: 23, Cr: 24, Mn: 25, Fe: 26, Co: 27, Ni: 28, Cu: 29, Zn: 30$)

Superconductors are derived from compounds of

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

The color of acidified $K_2Cr_2O_7$ is not changed by: