Wavelength of light used in optical instrument are $\lambda_1 = 4000 \mathring{A}$ and $\lambda_2 = 5000 \mathring{A}$, then ratio of their respective resolving powers (corresponding to $\lambda_1$ and $\lambda_2$) is :

Question

( A ) $4:5$
( B ) $16:25$
( C ) $5:4$
( D ) $9:1$