What is green revolution?When was it started?What are the advantages and disadvantages of green revolution?

The answer to the first part of your question has been covered in the NCERT solutions. You can find the answer in Chapter 2 (Indian Economy 1950-1990) - NCERT solutions- Question 7  

The answer to the second part of your question is as follows.

Probable Negative Impact of Green Revolution

The program of Green revolution had certain negative impacts as well.

1. Rise in the Inequality: The program was based on the use of certain key inputs such as the HYV seeds, chemical fertilisers, irrigation facilities, etc. The big farmers could easily afford such inputs and thereby, could reap the benefits of the program. As against this, the small and marginal farmers who could not afford such inputs suffered. As a result the gap between the big and the small farmers would increase. 

2. Vulnerability to Pest: The HYV crops were found to be more prone to pests. Thus, the vulnerability of the poor farmers dependent on this technology in terms of finance increased.