Wavelength of light used in an optical instrument are $\lambda_1 = 4000\,\AA$ and $\lambda_2 = 5000\,\AA$, then ratio of their respective resolving powers (corresponding to $\lambda_1$ and $\lambda_2$) is\\
(1) $16 : 25$\\
(2) $9 : 1$\\
(3) $4 : 5$\\
(4) $5 : 4$