1) The word "piano" contains three vowels: I, A, and O.

2) The President of the United States serves as the head of state and the head of government, responsible for leading the executive branch and representing the nation domestically and internationally.

3) The word "island" contains two vowels: I and A.

4) The role of the judiciary is to interpret laws, resolve disputes, and ensure justice in accordance with legal principles and the constitution. It serves as a check on the executive and legislative branches of government.