The correct options are
A Rajasthan has uneven population distribution because of the Thar desert.
C Sikkim has less population as it has a mountainous terrain.
D The population of Ladakh is less as it's too cold and mountainous.
Rajasthan has Thar desert and it's very difficult to grow anything in the desert region. Thus, there is very less population in the desert region. While Mumbai gets flooded with water, Nagpur hardly gets a high amount of rain. The population doesn't depend much on rainwater as nowadays there's a good water distribution channel. Population distribution does get affected by the terrain. If it's a mountainous region, transport becomes risky, and thus, not many people like to migrate to those places.