Can I use Kerosene for lubing the cogs and the chain I recently went to a bike mechanic and he dropped some kerosene on the cog and chain for lubing them. He said that it keeps the dirt off and is quite volatile so will evaporate after sometime leaving some part behind which acts as a good lube. He said that he knows this by experience. Is it good to use kerosene as lubricant?

No, Kerosene won't leave behind enough of a layer to protect the chain.

It might be useful as a solvent to clean the chain before applying a proper lubricant.