They have between 500-800 nuclear weapons, some of them thermonuclear. Unlike Iran, some of Israel’s nuclear missiles are installed on submarines, where it would be nearly impossible for anyone to get to them, so they have a second strike option. Only the US, Russia, China and UK have bigger arsenals.
“Only the US, Russia, China and UK have bigger arsenals.”
I think the UK only has a couple of hundred; China, 300 or so.