Suppose two objects are the same size. Must they weigh the same? Give an example to explain.

No. For example: take two beach balls. Fill one beach balls completely up with air. Then fill the other beach ball with water. Which one weighs more? Exactly the beach ball will water inside. Now that you have figured that out, playfully throw the beach balls at your best friend.

Not exactly just because they're the same size doesn't mean they weigh the same for example : a bowling ball and a soccer ball they are the same size don't exactly weigh the same