Here's why:

* Transition metals are defined as elements that have their d orbitals partially filled in their common oxidation states.

* Manganese (Mn), Chromium (Cr), and Osmium (Os) all fall within the d-block of the periodic table, and their common oxidation states involve partially filled d orbitals.

* Tin (Sn) is located in the p-block of the periodic table, meaning its outer electrons occupy p orbitals.

Let me know if you have any other questions!