Easiest fix ever: remove the bloody cheat sheet and make people actually remember stuff. Like, what, 99% of the other subjects?
While probably more fair, I think this would have a negative effect (certainly in the year the change occurred) because people would spend time memorising formulas and answers by rote instead and that would take away from solving physics problems. I do agree that the provided formula sheet should be all you need in a physics exam, and if the change was made then they could improve the current one. But it's not really an issue, I mean you're going to do better if you have some intuition behind a concept than if you 'just have it on your cheat sheet' for obvious reasons.
So for a 3 mark question, would we be expected to say for instance:
1 mark - whether it supports the wave or particle model
1 mark - why it supports the particle model (or vice versa)
1 mark - why it doesn't support the wave model (or vice versa)
??
Looks good to me, I'd say;
The experiment supports the wave model for light, as the pattern that is observed on the screen can be explained by diffraction and interference, both wave phenomena. It contradicts the particle model, which does not account for diffraction or interference, instead predicting two bright bands of light directly behind the slits.
Since the question seems to be geared towards a comparison, I'd chuck in a quick diagram of the two expectations if I had time! That's probably more than needed for 3/3, but it can't hurt to give more than required (as long as it's all correct)