Statement (i): The Indira Gandhi Canal project was conceived by Kanwar Sain in the early 1950s, but it was launched later in 1958, not 1961. Thus, this statement is incorrect.
Statement (ii): The introduction of canal irrigation in the command areas of the Indira Gandhi Canal project has indeed brought perceptible changes in the agricultural economy, especially through increased agricultural productivity. This statement is correct.
Statement (iii): The spread of canal irrigation in Rajasthan and the surrounding areas has led to an increase in both the cultivated area and crop intensity, particularly benefiting crops that require more water, such as rice and wheat. This statement is correct.
Statement (iv): Traditional crops like jowar and bajra, which were suited to the arid conditions, have been replaced by water-intensive crops such as rice and wheat due to the availability of irrigation. This statement is also correct.
Thus, only statements (ii), (iii), and (iv) are correct, making option (D) the right choice.