Photoelectric emission is observed from a metallic surface for frequencies \[{{v}_{1}}\] and \[{{v}_{2}}\] of the incident light rays\[\left( {{v}_{1}}>{{v}_{2}} \right)\]. If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of 1:k, then the threshold frequency of the metallic surface is

• A. \[\frac{{{v}_{1}}-{{v}_{2}}}{k-1}\]
• B. \[\frac{k{{v}_{1}}-{{v}_{2}}}{k-1}\]
• C. \[\frac{k{{v}_{2}}-{{v}_{1}}}{k-1}\]
• D. \[\frac{{{v}_{2}}-{{v}_{1}}}{k-1}\]