A, the balloon is in a state of balance, which is bound to be affected by the balance force. In the horizontal direction, the right hand points to the left and the left palm presses to the right. The balloon is in equilibrium, which means that these two forces are a pair of equilibrium forces, so they are equal. So, A is wrong.

B, from the pressure P=FS formula, under the same pressure, the greater the s, the smaller the pressure. The contact area between the left finger and the balloon is smaller than that between the right palm and the balloon, so the pressure of the right finger on the balloon is greater than that of the left palm, so B is correct.

C, according to the formula of pressure P=FS, under the same pressure, the greater the s, the smaller the pressure. The contact area between the left finger and the balloon is smaller than that between the right palm and the balloon, so the pressure of the right finger on the balloon is greater than that of the left palm, so C is wrong.

D the pressure inside the gas is related to the temperature, mass and volume of the gas. In this process, the mass and temperature of the gas remain unchanged, while the volume decreases, so the pressure increases. So, d is wrong.

So choose B.