Answer:
θ = 6.832 / a 10⁻⁷ rad
a= 1 mm, θ = 6.832 10⁻⁴ rad
Step-by-step explanation:
The limit of the resolution of a system is given by the first zero of the diffraction pattern for a slit is 
 a sin θ = m λ 
m = 1 
 a sin θ = λ 
 sin θ = λ / a 
 
in the case of circular tightness it must be solved in polar coordinates giving 
 sin θ = 1.22 λ / a 
 
as in diffraction experiments the angles are very small we can approximate the sine to the angle, in radians 
 θ = 1.22 λ / a 
 
Let's calculate 
 θ = 1.22 560 10⁻⁹ / a 
 θ = 6.832 / a 10⁻⁷ rad
 
In order to finish the calculation, the diameter of the objective lens is needed, for a sample let's use a diameter 1 mm = 10⁻³ m 
 θ = 6.832 10⁻⁴ rad