A transition metal exists in its highest oxidation state. It is expected to behave as

An oxidizing agent

The correct answer is option (3) an oxidizing agent.

Transition metals can exhibit a variety of oxidation states due to their ability to lose different numbers of d-electrons. When a transition metal is in its highest oxidation state, it means that it has lost a significant number of its electrons and is in a highly oxidized form. This high oxidation state generally means the metal ion is electron-deficient and has a strong tendency to gain electrons.

Here is why it behaves as an oxidizing agent:

High Electronegativity: In a high oxidation state, the metal ion is highly electronegative because it has lost many of its electrons and has a high positive charge. This makes it very attractive to electrons.

Electron Deficiency: The electron deficiency makes the ion highly reactive, and it tends to attract electrons from other species to achieve a more stable, lower oxidation state.

Reduction Potential: The metal in its highest oxidation state has a high reduction potential, meaning it has a strong tendency to be reduced by gaining electrons. When it gains electrons, it gets reduced, and the species donating the electrons gets oxidized.

Therefore, a transition metal in its highest oxidation state acts as an oxidizing agent because it readily accepts electrons, causing the oxidation of other substances.

For example, manganese in the +7 oxidation state (as in potassium permanganate, \( \text{KMnO}_4 \)) is a strong oxidizing agent. It accepts electrons to reduce to a lower oxidation state, such as +2, while oxidizing other substances in the process.