Option (A) Tamil Nadu is the correct answer. The provided text explicitly states that 'The groundwater utilisation is very high in the states of Punjab, Haryana, Rajasthan, and Tamil Nadu.' In contrast, the text mentions that states like Kerala utilise only a small proportion of their groundwater potential. Since Tamil Nadu is the only South Indian state listed among those with 'very high' utilisation in the context, it has the highest utilisation among the given options.