Apiano tuner knows that a key on the piano is tuned to the frequency of his tuning fork when he strikes them at the same time and the number of beats he hears each second is:
a) 0.
b) 1.
c) 2.
d) 3.
e) 4.

A) 0.

Explanation:

beats is the periodic variation in the loudness of a sound which is heard when two notes of almost the same frequency are played simultaneously.

Beats are used in tuning of musical instrument, e.g. a piano. To tune a piano, a piano tuner listens for beats produced between the sound from a standard tuning fork and that from a particular string on the piano when the piano key is struck. The tension in the piano string is adjusted until the beats disappear, i.e. when the frequencies are the same

Two tuning forks of frequency 256Hz and 254Hz are sounded simultaneously. Calculate the frequency of the resultant beat.

f == 2Hz

But in cases where beat is zero, it means the two notes are perfectly the same. This technique is used by a piano tuner to know that a key on the piano is tuned to the frequency of his tuning fork when he strikes them at the same time

NOTE : Hz means per second

because if the tool that you are using is not balanced it there would be false mass.