Henry Moseley studied the characteristic $X$-ray spectra of elements. The graph which represents his observation correctly is: (Given $\nu =$ frequency of $X$-ray emitted; $Z =$ atomic number)

The ratio of the radius of the first orbit in hydrogen to the radius of the first orbit in deuterium is .......

What is the ratio of the wave number of the first line (lowest energy line) of the Balmer series of the $H$ atomic spectrum to the first line of its Brackett series?

Which were the major problems before the scientists after the discovery of sub-atomic particles?

Which of the following statements are correct,if the threshold frequency of caesium is $5.16 \times 10^{14} \ Hz$?
$A.$ When $Cs$ is placed inside a vacuum chamber with an ammeter connected to it and yellow light is focused on $Cs$,the ammeter shows the presence of current.
$B.$ When the brightness of the yellow light is dimmed,the value of the current in the ammeter is reduced.
$C.$ When a red light is used instead of the yellow light,the current produced is higher with respect to the yellow light.
$D.$ When a blue light is used,the ammeter shows the formation of current.
$E.$ When a white light is used,the ammeter shows the formation of current.
Choose the correct answer from the options given below:

Bohr's atomic model explains the spectrum of only $.......$.