Which of the following constituents present in petroleum is responsible for ash formation?

In petroleum, the constituents responsible for ash formation are typically organometallic compounds. These compounds contain both organic (carbon-based) and metal components. During the refining process, when petroleum is subjected to high temperatures and pressure, these organometallic compounds can decompose and leave behind solid residues, forming ash.

Therefore, in this context, the correct option is Option B: Organometallic compounds.