The idiomatic phrase "have to" means "must" but may be shown as the slang term haveta.
The contraction (not a compound word) is doesn't.
The gaseous compound is "carbon dioxide."
Magnesium Sulfide
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The compound PbSO4 is lead sulfate, more specifically lead (II) sulfate.
That is the correct spelling of the compound noun "spacesuit."
The correct spelling of the compound noun is roommate.
That is the proper spelling of the compound word "frontiersman".
The word is spelled basketball. It is a compound word.
The correct spelling is "ammonia" (the chemical compound NH3).
The compound noun is spelled fishhook (a fishing hook).
The likely word is "vitamin" (necessary metabolic compound).