Answer
(a) Increasing the wavelength $\lambda$ would cause the fringe spacing to increase.
(c) Increasing the distance to the viewing screen $L$ would cause the fringe spacing to increase.
Work Step by Step
We can write a general equation for the fringe spacing $y$:
$y = \frac{\lambda~L}{d}$
(a) Increasing the wavelength $\lambda$ would cause the fringe spacing to increase.
(b) Increasing the slit spacing $d$ would cause the fringe spacing to decrease.
(c) Increasing the distance to the viewing screen $L$ would cause the fringe spacing to increase.
(d) Submerging the entire experiment in water has the effect of decreasing the wavelength, which would cause the fringe spacing to decrease.
