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

$KMnO_4$ is the oxo-salt of the acid of which of the following oxides?

Match Column $A$ with Column $B$:

Column $A$	Column $B$
$(1)$ Brass	$(a)$ $Ni$ $(60\%)$,$Cr$ $(40\%)$
$(2)$ Bronze	$(b)$ $Cu$ $(80\%)$,$Sn$ $(20\%)$
$(3)$ Cupronickel	$(c)$ $Cu$ $(90\%)$,$Sn$ $(10\%)$
$(4)$ Nichrome	$(d)$ $Cu$ $(70\%)$,$Zn$ $(30\%)$
	$(e)$ $Cu$ $(75-85\%)$,$Ni$ $(15-25\%)$

In $Cr_2O_7^{2-}$,every $Cr$ is linked to

Which among the following statements is incorrect for interstitial compounds?
$1$. They are very hard and rigid
$2$. They have higher melting point than pure metal
$3$. They do not show conductivity
$4$. They are chemically inert

Superconductors are derived from compounds of