The sound wave prodyced by a trumpet has a frequency of 440 hertz. What is the distance between successive compressions in this sound wave as it travels through air at STP?

Wavelength = (speed) / (frequency)

so in order to answer this question, we need the speed of sound.

Without using my precious time to go look it up, I'm guessing thatthe speed of sound at STP is roughly 343 m/s.

If that estimate is accurate, then

Wavelength = (343 m/s) / (440 / s) = 0.78 meter.

Choice-#2 is much closer to this result than any of the others, so choice-2 must be it.

Actually, we can 'reverse engineer' Choice-#2 and find the numberit uses for the speed of sound.

Speed = (wavelength) x (frequency)

= (0.75 m) x (440 / s) = 330 m/s.

The author of the question used 330 m/s for the speed of sound.