The correct answer is C. Needle exerts more pressure than nail on the balloon.
A nail is longer than a needle, but this does not mean that it exerts more pressure on the balloon. The pressure exerted by an object is equal to the force exerted by the object divided by the area of the object in contact with the surface. In this case, the force exerted by the nail and the needle is the same, since they are both being pushed into the balloon by the same person. However, the area of the needle is much smaller than the area of the nail, so the pressure exerted by the needle is much greater than the pressure exerted by the nail. This is why it is easier to burst a gas-filled balloon with a needle than with a nail.
Option A is incorrect because the length of the nail does not affect the pressure it exerts on the balloon.
Option B is incorrect because the nail and the needle exert the same force on the balloon.
Option D is incorrect because the gas in the balloon is not reactive with the needle.