A photochemical reaction requires `9.6 xx 10^(-16) J` energy per molecule of light with wavelength 250 nm that is just sufficient to intiate the reaction.

Answer

121 photons

Explanation

Wavelength of light ,
`lambda = 250 nm = 250 xx 10^(-9) m`
`E = (6.63 xx 10^(-34) xx 3.0 xx 10^8)/(250 xx 10^(-9))`
`= 7.956 xx 10^(-19) J`
Energy required per molecule
`= 9.6 xx 10^(-17) J`
No. of photons per molecule
`= (9.6 xx 10^(-17))/(7.956 xx 10^(-19)) = 121` photons