440 hertz = 440/seconds
1/440 seconds = period of the sound wave.
so Answer is 2.2727272* 10^-3 second or 1/440 seconds
Na is the symbol for sodium.
Rutherford found protons
Thompson found electrons and
Bohr crewed the Bohr model the most commen model of the atom used today
This really a your opinion question but my favor is Bohr