Explanation:

  Reasons of Rajasthan hot climate

Location:- Rajasthan as being in the inner part of the continent lack easily availability of moisture. In other words the Bay of Bengal branch get it's early retreat from Rajasthan.

Topography:- Topography of Aravalli mountains is such that it doesn't barricade the Arabian branch of S-W monsoon. This restrict moist air to form cloud as it will not get enough humidity to form clouds.

Lack of any big waterbody:- Rajasthan does not posses any big river or any lake which will provide enough moisture for a conventional rainfall.

Tropical location of Rajasthan:- However, this may be objectionable but because of clear sky conditions at tropics and it's location on tropic of cancer Rajasthan face direct action of sun's heat.

Altitude:- This is also a factor. If Rajasthan have had a good elevation then there could be cold conditions instead of hot.
All these factors are responsible in some way or other but the major reason for this is its topography of Aravalli mountains.