Statement 1 is correct. The onset of the Southwest Monsoon occurs in southern India (e.g., Kerala) typically by early June and then progresses northward across the subcontinent. The withdrawal of the monsoon, conversely, begins in the northern parts (e.g., Rajasthan) around September and proceeds southward. This pattern results in southern regions experiencing the monsoon for a longer duration (approximately four months) compared to northern regions, which receive monsoon rainfall for a shorter period (typically two to three months).
Statement 2 is correct. The amount of annual rainfall in the northern plains of India consistently decreases from east to west. This is primarily due to the Bay of Bengal branch of the Southwest Monsoon. As these moisture-laden winds move westward across the Gangetic plains, they gradually lose their moisture content through precipitation. Consequently, eastern parts of the plains (e.g., West Bengal, Bihar) receive significantly higher rainfall than the central (e.g., Uttar Pradesh) and western parts (e.g., Punjab, Haryana).
Options (1), (2), and (4) are incorrect because both statements 1 and 2 accurately describe established patterns of the Indian monsoon system. Option (1) is incorrect as it omits the correctness of statement 2. Option (2) is incorrect as it omits the correctness of statement 1. Option (4) is incorrect as both statements are factually valid.