How do 71% know Xenon is a gas, 50% for radon and only 48% for chlorine? It was the original gas used in World War One. Greenish-yellow clouds that people had no defense against so they'd urinate on a cloth and hold it to their airways to neutralize it.
It was a Canadian high school chemistry teacher who allegedly thought to urinate on a cloth whilst in the first gas attack on Ypres. But I don't think most people think of chlorine gas primarily in terms of World War I history.
Mr. Serico would be pround that all these years later, I still remember HONK-ull-briff (HONClBrIF) for the diatomic elements. 10-of-11. Krypton was my kryptonite.
Bromine and iodine also exist as gases at room temperature and standard pressure though their main forms are not gas.