I need help!! ~ 14 points

What property is a characteristic of a substance that can be observed and does not change the identity of the substance

What are the dimensions of the cross section that passes through the points a, f, g, and d?

There are multiple tuning forks present in the room, and annie strikes one with a natural frequency of 400 hz. which of these other tuning forks will begin to vibrate through resonance and make the sound louder? a 200 hz tuning fork a 400 hz tuning fork a 800 hz tuning fork a 1600 hz tuning fork