According to Bohr's principle,the relation between principal quantum number $(n)$ and the radius of the orbit $(r)$ is:

The emission spectrum of a gaseous atom is line-based and not continuous. Why?

When $\alpha$-particles are sent through a thin metal foil,most of them go straight through the foil because (one or more are correct)

What is the radius of the fourth orbit of a hydrogen atom (in $pm$)?

In the hydrogen spectrum,if an electron transitions from the $6^{th}$ orbit to the $3^{rd}$ orbit,what is the total number of spectral lines produced?

The energy associated with the electron in the first orbit of a hydrogen atom is $-2.18 \times 10^{-18} \ J$. The frequency of the light required (in $Hz$) to excite the electron to the fifth orbit is $(h = 6.6 \times 10^{-34} \ Js)$