Hydrogen

Step 1: Understanding the Concept:
Hydrogen economy refers to a proposed system of delivering energy using hydrogen as an energy carrier.

Step 2: Detailed Explanation:
The hydrogen economy envisions the use of hydrogen (dihydrogen, H ) as a clean, efficient fuel. It involves two key aspects: • Efficient production and utilization (conversion to energy via combustion or fuel cells). • Safe and effective storage and transportation (as compressed gas, cryogenic liquid, or in metal hydrides). Both points (a) and (b) are integral to the concept of the hydrogen economy.

Step 3: Final Answer:
Both (a) and (b) best describe the hydrogen economy, which corresponds to option (D).