Question

what is a gas bubble released at the bottom grows in size when it comes to the surface

Answer 1

The reason is that when a bubble is at the bottom of lake, total pressure exerted on it is the sum of the atmospheric pressure and the pressure due to water column. As the gas bubble rises, due to decrease in depth, the pressure due to water column decreases, so the total pressure exerted on the decreases. According to Boyle's law, the volume of the bubble increases due to the decrease in pressure, i.e. the bubble grows in size. When the bubble reaches the surface of the liquid, total pressure exerted on it becomes just equal to the atmospheric pressure only which is minimum and so the size of bubble on surface becomes maximum.