In order to factor this binomial, we need to find the common factors between each term.
Looking at the terms, we can see that each one has the factor 6ad^2.
Therefore, after factoring 6ad^2 from each term, we have:
[tex]\begin{gathered} 12a^3d^2−6ad^3\\ \\ =6ad^2(\frac{12a^3d^2−6ad^{3.}}{6ad^2})\\ \\ =6ad^2(2a^2-d) \end{gathered}[/tex]Therefore the correct option is the fourth one: 6ad^2(2a^2 − d)