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If λ₀ is the Threshold wavelength of a metal for photoelectron emission. If the metal is exposed to the light of wavelength λ, ​​then the velocity of ejected electron will be $\sqrt{\frac{2\mathrm{h}}{\mathrm{m}}({\mathrm{\lambda }}_0-\mathrm{\lambda })\mathrm{K}}$. The value of K is
(A) 1                 (B) $\frac{\mathrm{c}}{{\mathrm{\lambda }}_0\mathrm{\lambda }}$                 (C) $\frac{1}{{\mathrm{\lambda \lambda }}_0}$                 (D) $\frac{\mathrm{c}.\mathrm{\lambda }}{{\mathrm{\lambda }}_0}$