A slit of width a is illuminated by white light. The first minimum for light of wavelength 3900 Å will fall at θ = 60°, if a is

3900 Å 1950 Å 7880 Å 4503 Å

4503 Å

For first minimum, $a\sin θ = λ$ $⇒a=\frac{λ}{\sin θ}=\frac{3900}{\sin 60}Å=4503 Å$