Question

A hydrogen atom is in its elevnth excited state, n = 12. Using the Bohr model of hydrogen, find the linear momentum.

You want to solve for the electron velocity and multiply that by the electrn mass. There are many ways to do this. One would be to get the radius of the orbit from
R = 12^2 *a, where a is the first Bohr orbit radius. Knowing R, you can equate the centripetal force to the Coulomb force and solve for velocity. You may also be able to use a relation that says the number of de Broglie waves in the circular orbit is an integer (in this case, 12). The de Broglie wavelength is inversely related to the linear momentum, with Planck's constant as the factor.