What substances existed as solid flakes within the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form

none

Explanation: No substance exist as solid flakes within the innermost regions of the solar system before planets began to form. But substances that were found within the inner 0.3 AU of the solar system before planets began to form includes;rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form.