What is the longest wavelength λ of light that will provide photons of sufficient energy to break the π bond and cause the isomerization? express your answer numerically in nanometers?

Ans: The longest wavelength = 450nm (Approx)

Explanation:

Since,

λ=hc/E - - - (1)

where h=Plank's Constant=6.626x10^-34 Js

and c=Speed of Light = 3 x10^8 m/s

The energy to break a π bond = E = 4.42*10^-19 J/molecule

Substitute those values into equation (1):

λ = (6.626 x 10^-34) (3 x 10^8) / (4.42*10^-19)

λ=4.497*10^-7m

or (in nm)

λ=450nm (approx)