Correct Answer - B
Let, E = Energy falling on the surface per second `= 10 J`
Momentum of photons, `p = (h)/(lambda) = (h)/((c//v)) = (hv)/(c) = (E)/(c)`
On reflection, change in momentum per second `=` force
`= 2p = (2E)/(c) = (2 xx 10)/(3 xx 10^(8)) = 6.7 xx 10^(-8) N`