Let me explain you the laws of floatation

 

 

(i) The wt. of a body acts vertically downwards through centre of gravity of the body

 

(ii) The resultant upward thrust exerted on the body by the liquid i.e. force of buoyancy acts vertically upward through the centre of gravity of displaced liquid i.e. centre of buoyancy

 

 

(i) The wt of the body is equal to the wt. of the displaced liquid

 

(ii) The centre of gravity of the body and centre of gravity of the displaced liquid are in the same vertical line

 

The only essential condition for a body to float in a liquid is that the weight of the liquid displaced by the body should be equal to the weight of the body itself

 

Since air is pumped in side the water bottle, hence body will float until the wt. of the liquid displaced by the body is equal to the wt. of the body itself otherwise it will start submerge.