Final answer:
The state bounded by the Atlantic Ocean to the east and separated from Long Island to the south by the Long Island Sound is Connecticut.
Step-by-step explanation:
The state that has the Atlantic Ocean on its eastern border and is separated from Long Island to the south by the Long Island Sound is Connecticut. The Long Island Sound is a body of water that lies between the southern coast of Connecticut and the northern shore of Long Island, serving as a border between the two.
While Long Island is part of New York State, the Atlantic Ocean touches several states along the eastern coast of the United States, including Connecticut, which lies to the north of Long Island.