If the work function of a photo metal is 6.825 eV . Its threshold wavelength will be $\left(\mathrm{c}=3\times {10}^8\mathrm{m}/\mathrm{s}\right)$

• A

  1200 $\stackrel{\mathrm{o}}{\mathrm{A}}$

• B

  1800 $\stackrel{\mathrm{o}}{\mathrm{A}}$

• C

  2400 $\stackrel{\mathrm{o}}{\mathrm{A}}$

• D

  3600 $\stackrel{\mathrm{o}}{\mathrm{A}}$