KIDS TRIVIA

Detailed explanation-1: -Historically, concert pitch has varied. For an instrument in equal temperament tuned to the A440 pitch standard widely adopted in 1939, middle C has a frequency around 261.63 Hz (for other notes see piano key frequencies).

Detailed explanation-2: -Looking back at the piano chart image, we see that the C2 note has a frequency of 65.4 Hz and this frequency doubles at the next C note (C3) which is at 130.8 Hz (65.4 * 2 = 130.8). The frequency doubles again at C4 which is 261.6 Hz, and you can see that all octaves of all notes occur when the frequency doubles.