The characteristic X-rays wavelength is related to atomic number by the relation

$\sqrt{\mathrm{\nu }}=\mathrm{a}\left(\mathrm{Z}-\mathrm{b}\right)$

When Z is the atomic number, a and b are Mosley's constants. If ${\mathrm{\lambda }}_1=\mathrm{ }2.886\mathrm{ }\mathrm{Å}$ and ${\mathrm{\lambda }}_2=\mathrm{ }2.365\mathrm{ }\mathrm{Å}$ corresponding to ${\mathrm{Z}}_1=55$ and ${\mathrm{Z}}_2=60$ respectively, the value of Z corresponding to $\mathrm{\lambda }=2.660\mathrm{ }\mathrm{Å}$ is

• A

  63
• B

  67
• C

  74
• Correct answer
  D

  57

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