Which one of the following,when dissolved in water,gives a coloured solution in a nitrogen atmosphere?

In the reaction $4K_2Cr_2O_7 \xrightarrow{\text{heat}} 4K_2CrO_4 + 3O_2 + X$,identify $X$.

$A$ 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: $Sc: 21, Ti: 22, V: 23, Cr: 24, Mn: 25, Fe: 26, Co: 27, Ni: 28, Cu: 29, Zn: 30$)

Which transition metal oxide among the following has electrical conductivity similar to that of copper?

Which mineral among the following contains Vanadium in it?

In the reaction $4K_2Cr_2O_7 \xrightarrow{\text{heat}} 4K_2CrO_4 + 3O_2 + X$,the species $X$ is: