The focal lengths for violet, green and red light rays are ${\mathrm{f}}_{\mathrm{V}},{\mathrm{f}}_{\mathrm{G}}\text{ and }{\mathrm{f}}_{\mathrm{R}}$ respectively. Which of the following is the true relationship

• A

  ${\mathrm{f}}_{\mathrm{R}}<{\mathrm{f}}_{\mathrm{G}}<{\mathrm{f}}_{\mathrm{V}}$

• B

  ${\mathrm{f}}_{\mathrm{V}}<{\mathrm{f}}_{\mathrm{G}}<{\mathrm{f}}_{\mathrm{R}}$

• C

  ${\mathrm{f}}_{\mathrm{G}}<{\mathrm{f}}_{\mathrm{R}}<{\mathrm{f}}_{\mathrm{V}}$

• D

  ${\mathrm{f}}_{\mathrm{G}}<{\mathrm{f}}_{\mathrm{V}}<{\mathrm{f}}_{\mathrm{R}}$