In a thin prism of glass (refractive index 1.5),  which of the following relations between the angle of minimum deviations ${\mathrm{\delta }}_{\mathrm{m}}$ and angle of refraction r will be correct 

• A

  ${\mathrm{\delta }}_{\mathrm{m}}=\mathrm{r}$

• B

  ${\mathrm{\delta }}_{\mathrm{m}}=1.5\mathrm{r}$

• C

  ${\mathrm{\delta }}_{\mathrm{m}}=2\mathrm{r}$

• D

  ${\mathrm{\delta }}_{\mathrm{m}}=\frac{\mathrm{r}}{2}$