When an air bubble rises from the bottom of a lake to the surface it`s volume is doubled. Find the depth of the lake

dear rishabh 
the pressure at the bottom of lake = the pressure due to hot air + the pressure due to water column =P1. 
the pressure at the top is only the atmospheric pressure = P2 , 
initial vol = V1 , 
final volume = V2 . 
and after that u havenot mentioned anything about the temp . so, i am considering it to be constant 
so, from gas eq 
P1V1 = P2V2 
V2=2V1 
REST  u need to put the value , your ques seems incomplete as u have not mention the value . 
hope u understand the concept 
regards