A star is moving away from earth and shift in spectral line of wavelength 5700 Å is 1.90 Å. Velocity of the star is

$50\,km\,s^{-1}$ $70\,km\,s^{-1}$ $80\,km\,s^{-1}$ $100\,km\,s^{-1}$

$100\,km\,s^{-1}$

$Δλ=\frac{v}{c}λ$  $∴\frac{cΔλ}{λ}$ or $v=\frac{3×10^8×1.9×10^{-10}}{5700×10^{-10}}=100\,km\,s^{-1}$