Because it is covalent compound formed by sharing of electrons. Whereas, in other three compounds are ionic compounds & they conduct electricity in their molten state.

In the given question, u = – 30 cm and f = -20 cm. so, the object lies between F (20 cm) & C (40 cm). Therefore, a real image is formed beyond C, that is beyond 40 cm. Formula ...

As we know that, the oxygen during photo- synthesis comes from splitting of water molecules into hydrogen and oxygen gas.

A pure substances is one which is made up of only one kind of atoms or molecules. They have the same composition throughout.