The mass of a full bottle of cooking oil is 1.30 kg when half is empty calculate mass of empty bottle

Mass of bottle + cooking oil = 1.3 kg
Mass of bottle + 1/2 cooking oil = 0.9 kg
Thus half cooking oil = 1.3 - 0.9 
                                  = 0.4 kg
Mass of cooking oil in a full bottle = 0.4 × 2
                                                      = 0.8 kg
Therefore the mass of the empty bottle
               = 1.3 - 0.8 
               = 0.5 kg 

Rain is pulled by gravity which is a non contact force