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

Among the following oxides of $3d$ elements, the number of mixed oxides are . . . . . .
$Ti_{2}O_{3}, V_{2}O_{4}, Cr_{2}O_{3}, Mn_{3}O_{4}, Fe_{3}O_{4}, Fe_{2}O_{3}, Co_{3}O_{4}$

When copper turnings and concentrated $HCl$ are heated with copper sulphate,the compound formed is:

Consider the following reactions:
$K_2Cr_2O_7$ $\xrightarrow[-H_2O]{KOH} [A]$ $\xrightarrow[-H_2O]{H_2SO_4} [B] + K_2SO_4$
The products $[A]$ and $[B]$,respectively,are:

Which of the following substances will not give the borax bead test?

What is the oxidation state of osmium in $7B$ and $7C$,respectively?