Among the wavelengths emitted by iron atoms are λ = 500.572 nm and λ = 500.613 nm.

Among the wavelengths emitted by iron atoms are λ = 500.572 nm and λ = 500.613 nm. if we want to separate these two wavelengths clearly in the first order spectrum of a diffraction grating, what is the minimum number of lines that are required? if the spectral lines are observed in the second order spectrum also, calculate the number of lines required in this case.