In gold foil experiment number of deflected $\alpha -$ particles at angle $90^o$ is $63$ than number of $\alpha -$ particle deflected at $120^o$ is

In the spectrum of hydrogen atom, the ratio of the longest wavelength in Lyman series to the longest wavelength in the Balmer series is

Electrons with de-Broglie wavelength $\lambda $ fall on the target an $X-$ ray tube. The cut off wavelength of emitted $X-$ ray is

Energy levels $A, B$ and $C$ of a certain atom correspond to increasing values of energy, i.e. $E_A < E_B < E_C$ . If $\lambda _1, \lambda _2$ and $\lambda _3$ are the wavelengths of radiations corresponding to transitions $C$ to $B, B$ to $A$ and $C$ to $A$ respectively , which of the following relations is correct ?

The ratio of the speed of the electrons in the ground state of hydrogen to the speed of  light in vacuum is

The diagram shows the path of four $\alpha  - $ particles of the same energy being scattered by the nucleus of an atom simultaneously. Which of these are/is not physically possible