In Young's double-slit experiment, $12$ fringes are obtained on a certain segment of the screen when light of wavelength $600 \mathrm{nm}$ is used. If the wavelength of light is changed to $400 \mathrm{nm}$, the number of fringes observed on the same segment of the screen is given by

• Correct answer
  A

  $18$
• B

  $24$
• C

  $30$
• D

  $36$

Hence, the correct answer is option: 'A'.