Question

is the hardest known substance in nature
is a non-metal that is a good conductor of electricity.
5 Sihver objects turn black due to the formation of a layer of
on their surfaces​

Answer 1

Answer:

the hardest known natural substance is diamond and non metal that conduct electricity of electricity is is graphite

Answer 2

Answer:

Diamond is the hardest substance in. nature.

Graphite is a non metal but though a good conductor of electricity.

silver sulphide is form which turns silver into dull or black.