Chapter 2: Exploring Substances: Acidic, Basic, and Neutral

Acid Rain — Environmental and Heritage Threat

Normal rain has a pH of about 5.6 (slightly acidic due to dissolved CO₂ forming carbonic acid). Acid rain has a pH below 5.6, caused by sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) from burning fossil fuels reacting with atmospheric moisture to form sulphuric acid and nitric acid.

Effects:

• Damages forests and aquatic ecosystems (lakes become too acidic for fish)
• Corrodes buildings and historical monuments — the Taj Mahal has suffered marble cancer (kharna) due to acid rain from the Mathura Refinery and vehicle emissions. The Supreme Court's 1996 order (Taj Trapezium Zone case) restricted polluting industries within 10,400 km² around the Taj.
• Leaches nutrients from soil, reducing agricultural fertility

Soil pH and Agriculture:

• Most crops grow best at pH 6–7
• Acidic soils are treated with lime (calcium hydroxide or calcium carbonate) — a process called liming
• Basic/alkaline soils are treated with gypsum (calcium sulphate) or acidifying agents
• ICAR and state agriculture departments monitor soil health under the Soil Health Card Scheme (launched 2015) — tests soil pH, macro-nutrients (N, P, K), and micro-nutrients

Neutralisation in Daily Life:

• Ant bite (formic acid) → treated with calamine lotion (zinc carbonate, slightly basic)
• Indigestion (excess HCl in stomach) → antacids like milk of magnesia Mg(OH)₂
• Factory effluents (acidic) → neutralised with lime before discharge
• Swimming pool water → pH maintained at 7.2–7.8 using chemicals

[Additional] Ocean Acidification in Indian Waters — 2024 Research and India's Response (GS3 — Environment / Biodiversity):

Indian Ocean acidification data — 2024:

• Study: Chakraborty et al. (2024), Global Biogeochemical Cycles (American Geophysical Union) — first comprehensive multi-decadal acidification trend analysis for the Indian Ocean
• Arabian Sea: pH declining at -0.014 units per decade — among the fastest in the world's ocean basins due to warming-reduced CO₂ solubility combined with upwelling of CO₂-rich deep water
• Bay of Bengal: Similar declining trend but moderated by freshwater input from rivers (reducing salinity affects carbonate chemistry differently)
• Driver: Both CO₂ absorption from the atmosphere AND internal ocean circulation changes — India's monsoon system affects the Indian Ocean's carbon chemistry in ways that amplify the global acidification signal

Impact on India's marine ecosystems:

• Lakshadweep and Gulf of Mannar coral reefs: Already under dual stress — thermal bleaching (GCBE4 2024: Lakshadweep 84.6% bleached) AND structural weakening from acidification reducing calcification rates. These are not independent — acidification reduces the resilience of corals recovering from bleaching
• Gulf of Kachchh: India's most productive commercial fishery for shellfish (oysters, clams, crabs) — aragonite saturation decline threatens shell formation and growth rates
• Indian mackerel and sardine fisheries: Lower ocean pH affects the survival of fish larvae — larval fish use carbonate chemistry for calcification of otoliths (ear bones critical for navigation and schooling behaviour)

India's monitoring infrastructure:

• INCOIS (Indian National Centre for Ocean Information Services, Ministry of Earth Sciences): Operates carbonate chemistry monitoring as part of the INCOIS-ReML (Repeated Multipurpose Lines) programme — sampling across Arabian Sea transects; also the INCOIS-BIO-ROMS biogeochemical ocean circulation model
• NCSCM (National Centre for Sustainable Coastal Management, under MoEFCC): Runs CReON (Coral Reef in situ Observation Network) — autonomous buoys with sensors for temperature, pH, salinity, and dissolved oxygen at reef sites in Lakshadweep and Gulf of Mannar
• CMLRE (Centre for Marine Living Resources and Ecology, MoEFCC): Includes ocean acidification monitoring in its India-based marine biodiversity assessments

Policy gap:

• India has no dedicated national ocean acidification policy or action plan as of May 2026 — monitoring is spread across INCOIS, CMLRE, NCSCM without a unified framework
• A 2025 paper in iScience (Cell Press) by Indian researchers formally called for India to develop a national OA policy coordinated under MoEFCC — citing the gap between extensive monitoring data and absence of a regulatory or adaptation framework
• India's National Action Plan on Climate Change (NAPCC) and its missions (NMSA, NMSA, Green India Mission) do not explicitly address ocean acidification — a recognised policy omission

UPSC synthesis: Ocean acidification applies the chapter's core chemistry (CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻) at planetary scale — the same reaction that produces 5.6 pH rain is making the Arabian Sea 0.14 pH units more acidic per decade. The connection to India is direct: Indian Ocean acidification data is now available (Chakraborty et al. 2024), India's reef and fishery ecosystems are measurably affected, and India's institutional response (INCOIS + NCSCM + CMLRE monitoring) exists without policy integration. GS3 answers on ocean acidification can use this chapter's chemistry as the mechanism, India-specific data as the evidence, and the policy gap as the analysis.

[Additional] India's Soil Acidity Policy Response — ICAR Data and PM-PRANAM (GS3 — Agriculture / Environment):

Quantified soil acidification in India:

• ICAR-NBSS&LUP (National Bureau of Soil Survey and Land Use Planning) data: ~146.82 million hectares of India's total geographical area of 328.73 million ha classified as degraded; soil acidification identified as a major degradation type in eastern and north-eastern India
• ICAR Annual Report 2023-24: Approximately 49 million hectares of cultivated land in India has soil pH below 6.5 — requiring lime application for optimal productivity; ~30 million ha has pH below 5.5 (strongly acidic)
• North-east India: 7 states have predominantly acidic soils; Meghalaya, Mizoram, and Nagaland average pH 4.5–5.5 across most agricultural land — severely limiting crop diversity

Soil Health Card Scheme — current status (2024-25):

• Launched: February 19, 2015 (Rajasthan, by PM Modi)
• Scale: Over 23 crore Soil Health Cards distributed to farmers across three cycles (2015-17, 2017-19, 2019-23)
• Tests: 12 parameters — pH, electrical conductivity (EC), organic carbon (OC), N, P, K (primary nutrients), S, Zn, B, Fe, Mn, Cu (secondary/micronutrients)
• Implementing agency: Ministry of Agriculture and Farmers Welfare (MoAFW) through state departments
• Gap identified in evaluation: Card distribution is high, but uptake of recommendations (including lime application) remains low — NITI Aayog evaluation (2022) found only 30-40% of card recipients actually modified their input use based on recommendations

PM-PRANAM (PM Programme for Restoration, Awareness, Nourishment and Amelioration of Mother Earth):

• Launched: August 2023 (Union Budget 2023-24; MoAFW)
• Objective: Incentivise states and UTs to reduce chemical fertiliser use and shift to alternative, natural, and organic fertilisers — directly addressing the fertiliser-driven soil acidification problem
• Mechanism: States that achieve fertiliser subsidy savings (by reducing chemical fertiliser consumption) get 50% of the savings as a grant for further soil health promotion
• Nano urea and nano DAP: IFFCO's nano urea (liquid) approved by India (June 2021) and nano DAP (April 2023) as part of the PM-PRANAM goal to reduce soil acidification from conventional fertilisers
• Gobardhan scheme: Under PM-PRANAM umbrella — converts agricultural waste and cattle dung into biogas and organic manure, reducing synthetic fertiliser dependence

UPSC synthesis: Soil acidity connects the chapter's chemistry (acidic soil = pH < 7 → H⁺ and Al³⁺ toxicity → neutralised by calcium hydroxide liming) to India's most pressing agricultural challenge: nearly 49 million hectares of farmland are suboptimally acidic. The policy chain — Soil Health Card (diagnosis) → lime/gypsum application (neutralisation) → PM-PRANAM (reduce acid-forming fertilisers) → nano fertilisers (precision application) — is a complete GS3 agriculture answer framework. UPSC GS3 questions on soil degradation, fertiliser policy, or sustainable agriculture can use this chapter's neutralisation chemistry as the mechanism and India's specific soil acidity data as the evidence base.