Acalculate the wavelength of light emitted from the
hydrogen atom when the election undergoes a transition
from level n=3 to level n=1

What are the options? i can you if you give them.

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).