There’s the general crud around the hot plates, but the hot plates themselves keep getting rusty. And that’s melted plastic top left.
Elbow grease is going to be needed - that’s not a problem. But what else? I’ve tried scouring pads without much success but I’m wary of using harsher abrasives. You can just make out where I’ve scratched the ceramic below the left plate. That was using a steel scourer.
I take ‘hob’ to be the heating element for an electric range. I’ve never thought of cleaning one. I have a gas range. In the US the electric stovetop elements are coiled, not flat like that. I’d go careful, as to not damage it. I know you can replace the coiled ones. They just plug in.
I’m assuming that the actual heating element is something under those flat plates, since I can’t see how you would drive current through a disc to generate resistive heating. Assuming that is true, it seems like the flat plate must come off? So throw them in the sink and let them soak?
The rust would seem to imply that there was originally some sort of protective coating on the plates that has worn off. Can you treat them like a cast iron pan? Use something (steel wool?) to get the rust off, and then condition them with oil so they don’t rerust? I’ve never had a cast iron pan, so I’m mostly using words that I’ve seen in threads about them.
Otherwise, finding replacements seems a good choice.
For the melted plastic - if you’ve got an iron, can you put a cloth rag over the plastic, and then apply the hot iron to melt it and hopefully it absorbs into the rag (probably want a couple layers of cloth so it doesn’t get on your iron).
I managed to use a knife in the end. The flat blade meant that I didn’t damage the ceramic.
I have yet to try phosphoric acid on the hotplates but a mixture of caustic soda and vinegar followed by a dose of citric acid seems to have made an improvement.