Five definitions: hydrosphere, particulate matter, ecological pyramid, geothermal energy, e-waste

Any five of the six are answered; (v) is left out.

(i) The hydrosphere. The Earth's water in all its forms, from the oceans down to groundwater. It spreads over roughly three quarters of the planet's surface. Sea water makes up the bulk of it; fresh water, held in rivers, lakes, glaciers and underground aquifers and topped up again and again as water evaporates and comes back as rain, is only a small share.

(ii) Particulate Matter. Tiny solid particles that stay suspended in the air, such as soot from burning and the dust raised by traffic and construction; their effects range from dirty surfaces to cancer, in the case of asbestos fibres. Suspended particulate matter is counted among the five primary pollutants, which between them account for roughly nine-tenths of air pollution worldwide.

(iii) An ecological pyramid. A graph that stacks the trophic levels of an ecosystem one above another, each bar measured by the number of organisms, their biomass or the energy they hold; the producers make up the bottom tier and the top consumer the peak. The pyramid of energy can never be turned upside down, because some energy is lost as heat at every step. A pyramid of numbers or of biomass sometimes is: where a few large producers carry many small consumers, or where a small, fast-renewing stock of producers carries a larger stock of consumers.

(iv) Geothermal energy. Heat held inside the Earth: geo means earth and thermal means heat. Hot water drawn up from reservoirs deep underground is used to warm buildings, run industrial processes and generate electricity. That water often carries corrosive, polluting minerals, so it has to be treated before it is let out.

(vi) E-waste. Rule 3(1)(l) of the E-Waste (Management) Rules, 2022 defines it as "electrical and electronic equipment, including solar photo-voltaic modules or panels or cells, whole or in part discarded as waste, as well as rejects from manufacturing, refurbishment and repair processes". A dead phone charger or a broken laptop thrown out is e-waste.