Which of the following has conductivity and appearance like that of copper metal?

$CoO \cdot Al_2O_3$ is called

In making gun-barrel,the steel used is

$A \xrightarrow{4 KOH, O_2} 2 B (Green) + 2 H_2O$
$3 B \xrightarrow{4 HCl} 2 C (Purple) + MnO_2 + 2 H_2O$
$3 C \xrightarrow{H_2O, KI} 2 A + 2 KOH + D$
In the above sequence of reactions,$A$ and $D$,respectively,are:

When $MnO_2$ is fused with $KOH$,a coloured compound is formed. The product and its colour are:

The purple colour of $KMnO_4$ is due to the transition: