Which has more matter a ping pong ball or golf ball?

You know, I really don't know. But I can tell you how to find out.

Place water in a bowl and add the Golf ball. If it sinks, it's more dense, as it can't displace enough water to cause upthrust.

Do it carefully and measure the volume of water displaced, then weigh the dry ball and divide the grams by the cubic cm to get the density.

Easy.