Define a transition metal and explain its variable oxidation states.

A transition metal is defined as a d-block element that forms at least one ion with an incomplete d subshell. Transition metals exhibit variable oxidation states due to the involvement of d electrons in bonding, allowing them to lose different numbers of electrons.

This answer is strong because it clearly defines what a transition metal is and explains the concept of variable oxidation states, which is essential for understanding the chemistry of these elements. The question tests the student's ability to recall definitions and apply their understanding of oxidation states.