Answer
(a) smaller
(b) larger
(c) smaller
(d) larger
Work Step by Step
We can write an expression for the width of the spot:
$w = \frac{2.44~\lambda~f}{D}$
(a) Decreasing the wavelength of the light decreases the value of $w$
(b) Decreasing the lens diameter $D$ increases the value of $w$
(c) Decreasing the lens focal length $f$ decreases the value of $w$
(d) Decreasing the lens-to-screen distance causes the lens to move farther from the focal point. This increases the value of $w$
