Question

Rohit places a potted plant in a room in complete darkness after 3 days he takes out the plant and tests the leaf for the presence of starch will he get positive starch test give reason for the same

Answer 1

No.
Rohit won't get positive starch test because in the absence of sunlight plants won't be able to produce starch. 
 Leaves prepare glucose in plants with the help of photosynthesis which is later stored in the roots as starch or as energy stored. 
When there is no sunlight, the plant will not undergo photosynthesis thus no glucose, eventually no starch.