The problem of water pollution with Arsenic is maximum in

The correct answer is D, West Bengal. Arsenic contamination of groundwater is concentrated in the Ganga-Brahmaputra-Meghna alluvial plains, and West Bengal has the largest affected area and population in India. Districts such as Malda, Murshidabad, Nadia, North and South 24 Parganas and Howrah have groundwater arsenic well above the 0.01 mg/L limit set in IS 10500, which is the BIS drinking water standard.

• Haryana: Its groundwater problems are mainly salinity, nitrate and some fluoride. Arsenic is not a major widespread issue.
• Rajasthan: The dominant contaminants are fluoride, nitrate and salinity. Arsenic is not the leading problem.
• Madhya Pradesh: Its water quality concerns are fluoride and nitrate in some pockets, not arsenic at scale.

The core concept is geogenic arsenic released from sediments through reductive dissolution of iron oxides under anoxic conditions. This links to the Mains water and public health theme and to the arsenic mitigation approaches (deep tubewells, surface water supply, the National Programme on Arsenic in Groundwater) that are relevant for Environment and Governance answers. Bihar, Uttar Pradesh and Assam are also affected, so this is a ranking question where West Bengal leads.

Trap: Many aspirants pick Rajasthan because it is the first state they associate with groundwater pollution. In that state, the problem is fluoride, not arsenic.