Upto what frequency we can conclude something as a wave? I see here in my book electrons are considered as waves (using de-broglie's formula to find the wavelength of an electron)
I am calculating the wavelength of an electron for n=1 in hydrogen and it is coming a huge number of $334.01×10^3  m $.
So in this case should I still consider the electron to be a wave or not?
 A: Technically everything has a de Broglie matter-wave. The idea of “matter/wave duality” (google that) is that neither “particle” nor “wave” is completely and absolutely accurate at describing anything. Photons and electrons act like a particle and like a wave, such as in the slit experiment.
But wavelength decreases with resting mass. So youve calculated it incorrectly. The right answer should be in the nanometer range?
If something is big enough, certainly anything bigger than a big molecule, the wavelength becomes too small to ever matter, and treating it as matter is fine. But an electron is not big enough to ignore the wave aspect. In fact, the basis for electron shells at discrete energy levels in bohr’s model for atomic energy levels is that the electrons loop around the atom in a discrete numbers of waves, so as to have constructive self-interference.
If something is small enough for “the wave aspect” of it to possibly matter, then there might be a deliberate decision about whether to model it as a wave or particle. That decision often depends on what youre trying to figure out or solve.
