What is the number of waves formed by an electron in the $5^{th}$ Bohr orbit of a hydrogen atom?

The graph that depicts Einstein's photoelectric effect for a monochromatic source of frequency above the threshold frequency is

What is the wave number of the lowest energy transition in the Balmer series?

What is the radius of Bohr's fifth orbit for $B^{+4}$ in $\mathring{A}$ (in $.645$)?

Based on the equation $E = -2.178 \times 10^{-18} \ J \left( \frac{Z^2}{n^2} \right)$,certain conclusions are written. Which of them is not correct?

If the first emission in the Lyman series of a hydrogen atom occurs at $121.5 \ nm$,what will be the energy difference between the first and second orbits in $kJ/mol$?