Green fuels

Explanation

Statement 1 is correct: CORSIA is an ICAO-administered market-based measure (MBM) designed to address CO₂ emissions from international aviation. Airlines that emit beyond the agreed baseline are required to offset the excess, either by purchasing eligible carbon credits or by using CORSIA-eligible SAF, which generates offsetting units. Statement 2 is correct: SAF derives its carbon-reduction benefit from the lifecycle perspective — the CO₂ released on combustion is partly offset by the CO₂ absorbed when the biological feedstock (e.g. agricultural residues, waste oils) grew, resulting in a lower net lifecycle emission compared with conventional jet fuel. This lifecycle reduction is what CORSIA recognises and rewards. Statement 3 is false: CORSIA does not limit obligations to State/military aircraft; on the contrary, State aircraft (military, customs, police) are explicitly EXEMPTED from CORSIA. It is commercial international aviation that CORSIA targets. The 'pilot phase' (2021–2023) involved voluntary participation by States, but commercial carriers operating international routes between participating states were covered — not excluded. The statement inverts the actual exemption structure.

Explanation

Statement 1 is correct. CBG is produced via anaerobic digestion of organic material — including cattle dung, press mud, agricultural residue, and municipal solid waste. After purification and compression, it achieves a methane concentration of around 90–95%, making its calorific value essentially equivalent to fossil CNG, so it can substitute CNG directly in vehicles without engine modification. Statement 2 is correct. Under the SATAT scheme launched in 2018, private entrepreneurs and entities (including cooperatives and agro-processors) set up CBG plants and enter into agreements with OMCs to supply CBG. The OMCs market it through their retail fuel outlets. The scheme explicitly envisages that the residual fermented slurry — the digestate — be marketed as bio-manure or organic fertiliser, providing a second revenue stream alongside CBG sales, which is exactly the model Banas Dairy replicates under its Bhoomi Amrut brand. Statement 3 is incorrect. The energy content (methane yield) of biogas depends on the volatile-solids composition and biodegradability of the feedstock, not simply on whether it is livestock-based or crop-based. Agricultural residues such as rice straw do tend to have lower methane yields per unit mass compared to some livestock manures, but this is not an absolute rule — the yield depends on the specific substrate, C:N ratio, and digestion conditions. More importantly, SATAT and the national CBG framework are explicitly feedstock-agnostic and do not rank cattle dung as inherently superior in energy content to all agricultural residues; press mud from sugar mills, for instance, yields very high methane volumes. The statement's categorical claim is therefore a misconception.

Explanation

The classification of biofuels by generation is a standard framework in energy policy and biotechnology. First-generation biofuels are derived from edible food crops — sugarcane and corn for ethanol, palm oil and soybean for biodiesel — and are commercially mature but raise food-versus-fuel concerns. Second-generation biofuels use non-edible lignocellulosic feedstocks — agricultural residues (rice straw, bagasse), forest waste, and dedicated energy crops like switchgrass — avoiding direct competition with food supply but requiring more complex processing of cellulose and hemicellulose. Third-generation biofuels are based on microalgae: these photosynthetic microorganisms absorb carbon dioxide, grow rapidly, and accumulate significant quantities of lipids (oils/fats) that can be processed into biodiesel. The lipid accumulation in algae is notably enhanced under nutrient stress — particularly nitrogen deprivation — which is precisely the biological mechanism exploited by recent cultivation innovations. All three pairs are therefore correctly matched.

Explanation

Statement 1 is correct: green hydrogen is produced via electrolysis, wherein renewable electricity (from solar, wind, etc.) is used to split water (H₂O) into hydrogen and oxygen. This distinguishes it from grey hydrogen (produced from fossil fuels) or blue hydrogen (fossil-fuel-derived but with carbon capture). Statement 2 is incorrect: green hydrogen's primary targeted end-use sectors are industrial — steel manufacturing, chemical refining — and hard-to-abate transport sectors such as maritime shipping, aviation, and long-haul trucking. Electricity generation and residential heating are not the primary envisaged markets; in fact, direct electrification is generally more efficient for those end-uses. Statement 3 is correct: the water-energy nexus is a core constraint — the regions best endowed with solar and wind resources (arid, sun-rich zones) are frequently those with the least freshwater availability. This creates a structural trade-off: producing green hydrogen at scale in such regions requires either large volumes of freshwater (scarce locally) or energy-intensive desalination of seawater, each carrying ecological costs.