how will they evaluate the drawing paper in jee paer 2 for each question(50 marks for each picture) will it be tough correction ???

Usually they look for content based drawing in JEE MAIN PAPER 2 part III-Drawing test.

Meanwhile, this section is correctly the most meticulous section of the paper since students find it difficult to generate/draw given pictures very accurately in a particular time.
However it is seen that if one does good drawing in the section including the content based question(like using squares,quads make a meaningful drawing) then evidently they can score well in it.

Note:- It does not hamper your chances to get into any desired college of your choice. The overall marks achieved by you and the cutoff trends gurantee you for counselling. So don't be very worried.

2) For getting an architecture college in JEE MAIN P-2 one's rank should be less than 7000 for General/CRL merit list.