In my book Earth is said to be a very good conductor of electricity. Is it really a very good conductor? Many sources say that earth conducts electricity due to water and ions present in them. So it is a conductor but how can it be a very good conductor, sir? Further, is it a good conductor compared to most of the metals sir?
No, it isn't a good conductor. But it has a large cross sectional area. Remember that $R = \rho L/A$ so a large area means a low resistance even if $\rho$ is high.
@JohnRennie: When someone touches a power outlet standing on a concrete floor, he receives electric shock. How does concrete being an insulator conduct electricity sir? Further, I think it's not possible to complete a circuit using a concrete rod instead of a copper wire.
@JohnRennie :I tried that sir. I looked for conductivity of concrete, and other related questions. Even in PSE there was a similar question, but the answers don't address these. Only then I asked you sir.
Suppose I was standing in the sea, and touched an electric fence; I would receive an electric shock, because both my body and the sea are conductors, and create a path for the electricity to flow. The sea is so big that it has the capacity to draw and dissipate a great quantity of charge. However...