In the context of which one of the following are the terms ‘pyrolysis and plasma gasification’ mentioned?

The answer is D, waste-to-energy technologies. Pyrolysis is thermal decomposition of organic matter in the absence of oxygen, which yields syngas, bio-oil and char. Plasma gasification uses an electric plasma arc, at several thousand degrees, to break waste down into syngas and inert vitrified slag. Both convert municipal, plastic or biomedical waste into usable energy or fuel, so they belong to the waste-to-energy family.

Why the others fail:

• A Rare earths come from mining, beneficiation and solvent extraction or ion exchange. Pyrolysis and plasma have no role there.
• B Natural gas is extracted by drilling and, in shale, hydraulic fracturing. Gasification of waste is a different process, and the word 'gasification' does not make it a gas-extraction method.
• C Hydrogen vehicles depend on electrolysis, steam methane reforming or fuel cells. Pyrolysis is not the framing technology for this option.

On the Mains side, this links to GS-3 on solid waste management, the Solid Waste Management Rules, circular economy and the energy-from-waste debate, including concerns about emissions and dioxins from poorly run plants.

Trap: Aspirants who treat 'gasification' as a fossil-fuel term pick B. Remember that these are thermochemical waste conversion routes.