Two charges placed in air repel each other by a force of ${10}^{-4} \mathrm{N}$. When oil is introduced between the charges, the force becomes $2.5\times {10}^{-5} \mathrm{N}$. The dielectric constant of oil is

• A

  2.5

• B

  0.25

• C

  2.0

• D

  4.0