Question

what happens the harder you strike a guitar string?
the sound has a higher pitch.
the sound is louder.
the sound is quieter.
the sound has a lower pitch.

Explanation:

When you strike a guitar string harder, the amplitude of the vibration increases. Amplitude is related to the loudness of the sound. A higher amplitude means a louder sound. Pitch is related to the frequency of the vibration, which is not affected by how hard you strike the string (assuming the string's length, tension, etc., remain the same).

Answer:

The sound is louder.