Israel will respond with a nuclear attack if it is attacked by nuclear weapons; so said Ben Guryon. Israel will use nuclear weapons in a desperate situation; and there is no doubt, as Golda Mair almost did in the war with Egypt. I doubt that a gas attack would trigger a nuclear attack; it depends on how successful it proves to be. Israel's enemies have to calculate, a nuclear attack by Israel would destroy them and that is Israel's great strength. Moreover Israel has fusion bombs and Iran can only have wet dreams about such weapons.
Shaffir to Herzog: Opposition failed to show leadership in political battles against PM (Haaretz)
from the article: Israel's enemies wouldn't dare launch chemical attack, Barak says