Ask two jokes about ninth grade chemistry! Better be simple and easy to laugh!

Some experts put forward a chemical problem: 1 and 2 can be transformed into each other. 2 Boiled water becomes 3.3, which reacts with the gas in the air, and 4 and 4 will have the smell of rotten eggs. Experts say: 1, 2, 3, 4, what's the difference! The high flyer said: 1. It is a hen. 2. This is an egg. This is a hard-boiled egg. 4. It's rotten eggs. Hydrogen sulfide smells like rotten eggs.