The answer to this is Chlorine. Chlorine is one of the most well-known elements probably because it is being used for a lot of purposes. A lot of our drinking water is treated a bit with chlorine so that it will be safe to drink. Chlorine is also used in a lot of swimming pools to keep it clean for a longer period of time. There are a lot of factories that would need chlorine for a variety of purposes.
For example, there are some that can be used for paper, some can be used for plastic, some are even used for medications. Chlorine is known to be rampant and it is definitely useful.