Solve the equation using a an equation; 
Energy(E)= Nhv= N1hc/I 
Where N= no of photos; 
H=planks constant ;c= velocity of light and 
I= wave length 
Thus here, 
N1hc/I1=N2hc/I2 
Or, N1/I1=N2/I2 
Let N1=no of photon in 1.0 mol of ir radiation =6.028*10^23;I1=1000 nm 
Then N2=?; I2=400 nm 
Hence, 
N2=N1*I2/I1 
6.02*10^23*400/1000 
=0.4*6.02*400/1000 
=0.40 mol of uv