If the radius of first Bohr's orbit of hydrogen is $\text{x}$, then the de-Broglie wavelength of the electron in its $3^{\mathrm{rd}}$ orbit is

• A

  $2\mathrm{\pi }\mathrm{x}$
• Correct answer
  B

  $6\mathrm{\pi }\mathrm{x}$
• C

  $9\mathrm{x}$
• D

  $\frac{\mathrm{x}}{3}$

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