The correct answer is indeed option 1, which states that an air bubble will increase in size as it rises from the bottom of a lake to the top. Here`s why this is the case:

Option 1 is correct because the pressure decreases as you go up in the water body. Hence, the air bubble experiences less pressure as it rises and hence it expands or increases in size.

Option 2, `decrease in size`, is not correct because as explained, the pressure decreases as the bubble rises, not increases; thus, the volume of the bubble increases, not decreases.

Option 3, `maintain its size`, is also incorrect. The pressure acting upon the bubble changes as it rises or falls in the water, causing the bubble to change size.

Option 4, `flatten into a disk-like shape`, is incorrect. While the shape of the bubble might change slightly due to the change in pressure, it does not flatten. The air bubble tries to maintain a spherical shape because a sphere minimizes surface area and it`s the most energy-efficient shape.