Consider the following activities : 1. Spreading finely ground basalt rock on farmlands extensively 2. Increasing the alkalinity of oceans by adding lime 3. Capturing carbon dioxide released by various industries and pumping it into abandoned subterranean mines in the form of carbonated waters How many of the above activities are often considered and discussed for carbon capture and sequestration?

Answer: C. All THREE activities are discussed for carbon capture and sequestration (CCS). (1) Spreading finely ground basalt on farmlands (enhanced weathering): CORRECT. This 'enhanced rock weathering' approach uses crushed silicate rocks like basalt. Basalt minerals naturally absorb atmospheric CO2 by reacting with water and CO2 to form stable carbonate minerals. Spreading on farmland accelerates this; co-benefits include improved soil fertility. Project Vesta and others are testing this at scale. (2) Increasing ocean alkalinity by adding lime: CORRECT. Ocean alkalinity enhancement is a proposed CCS approach. Adding crushed limestone or quicklime to ocean water increases pH and dissolved bicarbonate, drawing CO2 from the atmosphere into stable oceanic carbonate. Concerns include scale, energy and ecological effects. (3) CO2 injection into abandoned subterranean mines as carbonated water: CORRECT. CO2 sequestration via injection into deep geological formations (depleted oil/gas reservoirs, saline aquifers, abandoned mines) is a mature CCS approach. Injecting CO2 as carbonated water enhances mineral carbonation, locking CO2 as solid carbonates over time. Source: IPCC AR6 Climate Change 2022 / IEA CCUS reports.