Which oxide of transition metals exhibits electrical conductivity as high as that of metals?

The colour of the bead in the borax bead test is mainly due to the formation of:

The orange-red color of an aqueous solution of $K_2Cr_2O_7$ changes to lemon yellow when treated with aqueous $KOH$. What is the reason for this?

On heating a mixture of common salt and $K_{2}Cr_{2}O_{7}$ with concentrated $H_{2}SO_{4}$, a gas is evolved. The formula of the gas evolved and the oxidation state of the central metal atom in the gas, respectively, are:

Fill in the blanks:
$(1)$ ......... acid is added to perform titrations with $KMnO_4$ and $K_2Cr_2O_7$.
$(2)$ Crystals of potassium dichromate are of ......... color,while crystals of potassium chromate are of ......... color.
$(3)$ The color of $MnO_4^{2-}$ is ......... and the color of $MnO_4^-$ is ......... .

Sodium chromate,$Na_2CrO_4$ is made commercially by