Understanding the difference between physical and chemical changes Which of the following is a chemical change?
A. Hydrolysis of a dipeptide.
B. Stretching of a balloon.
C. Freezing of water.
D. Breaking a stick.

I'm pretty sure that the answer is (A), but I'm not 100% positive.
I know that, for (C), you can freeze water, and then you can melt it back to liquid water.
For (D), you can break a stick, and the stick is still now two sticks.
For (B), however, I think that it is a physical change, but I'm not entirely certain.
Can someone please explain this for me?
Yes, (B) is a physical change. Stretching the balloon simply rearranges the polymer strands in the balloon material, making them straighten out instead of being kinked up. When you let the balloon go, they just pull back to their former kinked shape.

Your reasoning on (C) and (D) is solid.

The answer is indeed (A). See Wikipedia's page on hydrolysis for more information.