In India, the single largest contributor of greenhouse gas emissions among the given industries is the power industry.

Option 1: Cement industry is not the largest contributor, as it is not mentioned in the correct answer.

Option 2: Fertilizer industry is not the largest contributor, as it is not mentioned in the correct answer.

Option 3: Power industry is identified as the correct answer. Power generation in India heavily relies on coal, which is a major source of greenhouse gas emissions. This industry emits a significant amount of carbon dioxide and other greenhouse gases due to the combustion of fossil fuels for electricity production.

Option 4: Steel industry is not the largest contributor, as it is not mentioned in the correct answer.

In conclusion, the power industry in India is the leading contributor of greenhouse gas emissions, primarily due to its reliance on coal for electricity generation.