What is unique about rhode island?

Answer 1

Rhode Island did not provide representation to assist in framing that document. They sat out the Constitutional Convention in protest insisting that a Bill of Rights and some form of protection for small states had to be included before they would be a party to the proposed Constitution. They got their way with a bi-cameral Legislature where the small states were equals in the upper house and assurances that a Bill of Rights was to be added to the Constitution. They ratified the US Constitution and joined the United States on 29 May 1790.

Answer 2

it is extremely small.