(i) North India lies away from the water bodies and experiences continental type of climate whereas South India being near the water bodies experiences maritime climate. Also, North India comes in temperate zone as it lies towards the north of Tropic of Cancer whereas South India falls in Torrid Zone towards the south of Tropic of Cancer. Due to these reasons, North India has a greater range of temperature than South India.
(ii) The temperature of Delhi is less than that of Chennai in December because Delhi lies beyond the Tropic of Cancer, in the Temperate zone. So in December, it receives slanting rays of the sun. But Chennai is located in Torrid zone and hence, it receives vertical rays of the sun throughout the year. Therefore, the temperature of Delhi is lesser during the December.
(iii) Desert areas experience a high day temperature and a much lower night temperature because desert areas are covered with sand. The physical property of the sand is to get heated up quickly and cool down abruptly. So, the day temperature is very high and the night temperature is very low.