Detailed Explanation:

Answer: Option 3 — All three

Green hydrogen, produced through electrolysis of water using renewable electricity, is expected to play a significant role in decarbonizing all three heavy industries mentioned. It offers a clean alternative to fossil fuels in energy-intensive industrial processes, thereby reducing carbon emissions substantially.

1. Fertilizer plants: Green hydrogen can replace natural gas in ammonia synthesis, which is the primary feedstock for fertilizer production. This eliminates the carbon-intensive steam methane reforming process currently used.

2. Oil refineries: Refineries use hydrogen for hydrocracking and desulfurization processes. Green hydrogen can replace the hydrogen currently produced from fossil fuels, reducing the refinery's carbon footprint.

3. Steel plants: Green hydrogen can replace coal and coke in the direct reduction of iron ore (DRI process), eliminating one of the largest sources of industrial CO₂ emissions. Several pilot projects globally are already testing hydrogen-based steelmaking.

📝 Short Notes: Green Hydrogen and Industrial Decarbonization

• Green Hydrogen: Hydrogen produced via electrolysis of water using electricity from renewable sources (solar, wind, hydro). It is carbon-free if the electricity is 100% renewable.
• Fertilizer Industry: Uses hydrogen to produce ammonia (NH₃) via the Haber-Bosch process. Currently, ~1-2% of global energy and CO₂ emissions come from ammonia production using fossil fuel-derived hydrogen.
• Oil Refining: Refineries consume significant hydrogen for upgrading heavy crude, hydrocracking, and removing sulfur. Green hydrogen can directly substitute fossil-fuel-derived hydrogen.
• Steel Industry: Traditional blast furnace method uses coke (from coal) as a reducing agent. Green hydrogen-based Direct Reduced Iron (DRI) technology can replace this, producing water instead of CO₂.
• National Green Hydrogen Mission (India): Launched in 2023 with ₹19,744 crore outlay to make India a global hub for green hydrogen production and export by 2030.
• Challenges: High production cost, infrastructure development, storage and transportation issues, and scaling up electrolyzer manufacturing capacity.