Answer:
1.9×10^20
Explanation:
ϕ = number of reaction events /number of photons absorbed
ϕ= 0.26
Energy= power× time
885×10^-3×10×60= 531J
But E= nhc/λ
n= number of photons
h= planks constant
c= speed of light
λ= wavelength
n= Eλ/hc
n= 531×280×10^-9/6.6×10^-34 ×3×10^8
n= 7.5×10^20
Therefore
From
ϕ = number of reaction events /number of photons absorbed
Number of reaction events= 0.26×7.5×10^20
= 1.95×10^20