What kind of gases did World War 2 gas masks protect us from?

The ww2 headmasks protected us from any type of poisonous gas the enemies had dropped from the sky. Like an explosion, they told us to duck, and cover.

In WW1, mustard gas was used as a weapon of mass destruction as I have seen on documentaries. I do not recall what types of gases were used during WW2 in battle although many innocents were killed in concentration camps using poisonous gas. Because of its vile nature combatants have not used gas on one another at least as far as the media and governments allows us to know. A form has been used last however by the military of Iraq on the kurdish population as reported on the news. It was a terrible, terrible thing that was done. This was before the overthrow of Saddam Hussein.

Another gas that was used in WWII, was Carbon Monoxide, a poison that could travel airborne, was invisible, and had absolutely no color, so it was ideal for suprise attacks.