The frequencies of notes given by flute, guitar and trumpet are respectively $ 400Hz $ , $ 200Hz $ and $ 500Hz $ . Which one of these has the highest pitch?

Hint: As we can see here that there are two terms of importance that are the frequency and the pitch. We will be discussing these both terms and will find the relation between them.

Complete step by step answer:
What do we mean by frequency? Frequency is nothing but the number of occurrences of a repeating event per unit of time. In short, it is the number of cycles completed in a unit period of time. The unit of frequency is Hertz

As in sound waves, the number of cycles completed in a unit period of time is its frequency.
Now we come to the discussion of the pitch of the sound. When you listen to music, you hear both high and low sounds. The characteristic of highness or lowness of a sound is called pitch. The frequency of a sound wave determines the pitch of the sound you hear.
Till now we should get to know that frequency can also be defined as the number of waves passing a fixed point in a given period of time. If the frequency of the sound wave is high, then the corresponding sound will be high and hence, we can say that the pitch of the sound is high and vice versa.

Wave of a low pitch sound.

Wave of a high pitch sound.
Hence, we can say that the pitch is directly proportional to the frequency.
Now, as we can see in the above example, the note corresponding to the highest frequency is given by the trumpet, i.e., $ 500Hz $ .
Therefore the note of the trumpet has the highest pitch among the others.

Note:
The frequency and the pitch of the sound are directly proportional to each other. If the wavelength is given in place of the frequency, then the pitch is inversely proportional to the pitch of the sound .i.e., higher the wavelength, the lower will be the pitch of that signal.