Melting might work on the Wicked Witch of the West but with zombies it rarely works out. There are a lot of reasons for this but the most obvious is that you just don’t have anything at hand to do it with. Sure you could probably get some chemicals and mix something up if you were good at chemistry but it’s hard to keep that stuff on hand, hard to apply it to the zombie, and hard to keep from getting injured yourself. All those chemicals could get splashed back on you if the zombie thrashes around at all and you’re going to have a hell of a mess on your hands if that thing was inside your bunker. Dumping acid on zombies is something similar to boiling oil being dropped on knights during the middle ages. It requires a structure through which the zombies would have to pass and then have the stuff dropped on them and you’re not likely to have any of that. What you’re going to have are little mason jars that need to be flung at the zombies, the success of which depends entirely on your aim.