What are some main points about the Bhopal diaster that could go in an essay?

This depends to some extent on what you want your essay to
be about.  You could go in a number of directions.  For example, you could discuss any
or all of the following:

• The extent of damage
  done and the plight of the survivors.  You could focus your essay on a description of
  how bad the disaster was and on what was done or not done to help the
  victims.


• The actions or inactions of the Indian
  government that allowed the disaster to happen.  You could research the extent to which
  the government did or did not try to ensure that the Union Carbide plant would be
  safe.


• The degree to which Union Carbide itself was
  responsible for the disaster.  You could look at the evidence that shows that the
  company was aware that the plant was dangerous.  You can try to account for why the firm
  did not do more to ensure that the plant was
  safe.

These are some areas that you might
address.  Please follow the link for good details on the circumstances surrounding the
disaster.