Among the following, which one is the least water-efficient crop?

Sugarcane requires approximately 210 liters of water to produce 1 kg.

The water footprint of sunflower is significantly lower, around 7-9 liters per kg.

Pearl millet is cultivated in dry regions and requires minimal irrigation.

Red gram needs about 35-40 cm of water throughout its growth cycle and is typically grown as a rain-fed crop in areas with sufficient rainfall, thus usually not requiring irrigation.

Therefore, sugarcane is the least water-efficient crop among the options.

Hence, option (a) is the correct answer.