<span>The sum of the protons and neutrons in an atom equals the mass number. </span>
It represents where it is located in the periodic table and how many protons a element has.
Length of the sheet is given as

width of the sheet is given as

now let say its thickness is "t"
so the volume of the sheet is given as



mass of the sheet is given as

now we have


by solving above we have

so the thickness of sheet will be above
The whistle you use to call has a frequency of 21 kHz, so you do not recognize it also because your threshold of hearing is only 20 kHz. Since you are unable to hear sounds above this value, you request your friend to blow the whistle and move farther away. The frequency will decrease due to Doppler effect.
Explanation:
Introduction to the quantum mechanical model of the atom: Thinking about electrons as probabilistic matter waves using the de Broglie wavelength, the Schrödinger equation, and the Heisenberg uncertainty principle. Electron spin and the Stern-Gerlach experiment.