Which of the following is an example of a sublimable solid? MCQ with Answer and Explanation

Explanation:
Complete combustion of ethanol: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat. In sufficient oxygen, carbon burns to CO₂, hydrogen to H₂O. Incomplete combustion (lack of O₂) produces CO and soot (C). Ethanol is a biofuel, reducing CO₂ emissions if derived from biomass. It has high octane number and is blended with petrol (gasohol). CO₂ is a greenhouse gas, but bioethanol is carbon-neutral over cycle.

Explanation:
Biofuels are produced from biomass—recently living organisms or their metabolic byproducts. Examples: ethanol from sugarcane/corn, biodiesel from vegetable oils, biogas from organic waste. They are renewable and can reduce greenhouse gas emissions compared to fossil fuels. However, large-scale production may compete with food crops. Algae-based biofuels are also being researched.

Explanation:
Azotobacter is a free-living aerobic bacterium that fixes atmospheric nitrogen in the soil, making it available to non-leguminous crops. Rhizobium is symbiotic and specific to legumes. Nitrobacter and Nitrosomonas are involved in nitrification (converting ammonia to nitrites/nitrates), not nitrogen fixation.