Heteropoly acids are formed by?

Mo

Heteropoly acids are a type of polyoxometalates, which are compounds that contain metal cations coordinated to oxygen atoms. These acids are typically composed of a central metal atom, such as molybdenum (Mo), surrounded by oxygen atoms and other heteroatoms, such as hydrogen and other non-metal atoms.

Molybdenum (Mo) is well-known for forming a wide range of heteropoly acids. These acids are formed by the combination of molybdenum with oxygen and other elements, typically in an acidic medium. The resulting heteropoly acids have unique structures and properties that make them important in various chemical and catalytic processes.

Therefore, the correct answer is (2) Mo, as heteropoly acids are primarily formed by molybdenum.