The correct answer is b) July.
Kerala receives the highest rainfall during the southwest monsoon season, which runs from June to September. The monsoon rains are caused by the seasonal shift in the Intertropical Convergence Zone (ITCZ), a band of low pressure that lies near the equator. During the southwest monsoon, the ITCZ moves northward over India, bringing with it moisture-laden winds from the Arabian Sea. These winds rise up the Western Ghats, the mountain range that runs along the western coast of India, and cool, causing the water vapor to condense and fall as rain.
The southwest monsoon is the most important source of rainfall for Kerala. The state receives an average of 3,000 mm of rain per year, with most of the rain falling during the monsoon season. The monsoon rains are essential for agriculture and other water-dependent activities in Kerala.
The other options are incorrect because they are not the months during which Kerala receives the highest rainfall. June is the beginning of the southwest monsoon season, but the rainfall is not as heavy as it is in July. August is the peak of the monsoon season, but the rainfall starts to decrease in September. September is the end of the monsoon season, and the rainfall is very light.