Which element does most of the polyatomic ions contain?

Polyatomic ions are the ions containing more than one atom. Most polyatomic ions contain oxygen.

The names of the polyatomic ions containing oxygen end in "ite" or "ate". For example - $N{O}_3^{-}$ ion is called nitrate, $S{O}_3^{2-}$ ion is called sulphite, $S{O}_4^{2-}$ ion is called sulphate, $C{O}_3^{2-}$ ion is called carbonate and many other such polyatomic ions exist.

The table attached above shows various polyatomic ions, and we can see that oxygen is the most common element in them.