In a photo-emissive cell, with exciting wavelength X, the fastest electron has speed v. If the exciting wavelength is changed to \[\frac{5\lambda }{4}\], the speed of the fastest emitted electron will be

• A. \[{{\left( 3/4 \right)}^{1/2}}.v~\]           
• B. \[{{\left( 4/5 \right)}^{1/2}}.v\]
• C. less than \[{{\left( 4/5 \right)}^{1/2}}.v\]
• D. greater than \[{{\left( 4/5 \right)}^{1/2}}.v\]