What is the smallest separation between two slits that will produce a second-order minimum for 762 nm red light?

1524 nm.

Explanation:

Angular separation of n th minima is given by the expression

Sin θ = n λ / a

Where λ is wavelength of light used and a is separation between two slits .

a = n λ / sin θ

For a to be minimum, sinθ has to be maximum .

maximum value of sin of any angle is 1 .

so the relation becomes as follows

a = n λ

n = 2 , λ = 762 nm.

a = 2 x 762 nm

= 1524 nm.

an obstruction