The correct answer is (a) Gujarat.
Gujarat has the largest area of alkali soils in India, covering about 10 million hectares. These soils are found in the northern and central parts of the state, and are characterized by high pH levels, low organic matter content, and poor drainage. Alkali soils are difficult to cultivate, and often require special management practices to improve their productivity.
Haryana, Punjab, and Uttar Pradesh also have significant areas of alkali soils, but these are not as extensive as those in Gujarat. In Haryana, alkali soils are found in the southern and western parts of the state, while in Punjab they are found in the central and eastern parts. In Uttar Pradesh, alkali soils are found in the western and eastern parts of the state.
Alkali soils are a major problem in India, as they reduce crop yields and make it difficult to grow certain crops. The government of India has implemented a number of programs to address the problem of alkali soils, including the development of new varieties of crops that are tolerant of alkali soils, and the construction of drainage systems to improve the drainage of alkali soils.