What is shown by Thomson's experiments of electric discharge through gases ? And explain the plum pudding model.

Give a powerful way to determine an upper limit to the size of the electron.

The wavelength of ${K_\alpha }$ line for an element of atomic number $29$ is $\lambda $ . Then the wavelength of ${K_\alpha }$ line for an element of atomic no $15$ is (Take mosley‘s constant $b = 1$ for both elements)

Hydrogen atom is excited from ground state to another state with principal quantum number equal to $4$. Then the number of spectral lines in the emission spectra will be

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