Option A: Due to the increase in the height of the atmosphere, the size of the balloon will decrease. As the balloon rises, the atmospheric pressure decreases. Since the pressure inside the balloon remains constant due to the ideal gas law, the gas molecules inside expand to occupy more space. However, the balloon’s material constrains this expansion, causing it to stretch and decrease in size. Therefore, the balloon appears to shrink as it ascends. Option B (The balloon will flatten and come in the shape of a disc) is incorrect because the balloon’s shape is determined by its elasticity and the pressure difference between the inside and outside. As the pressure inside remains constant, the balloon’s shape won’t flatten into a disc. Option C (The size of the balloon will increase) is also incorrect because, although the gas inside expands, the material constrains this expansion, causing the balloon’s size to decrease. Option D (The size and shape of the balloon will remain the same as before) is inaccurate because the balloon’s size decreases due to the pressure difference between the inside and outside as it ascends through the atmosphere. Therefore, option A, the size of the balloon will decrease, is the correct choice.