In a federal state, the powers of the central government and the state governments (also known as constituent units) are clearly defined and laid down. This means that there is a clear division of powers between the central government and the state governments, and each level of government has its own set of responsibilities and authority.

Option 1 states that the clear division of powers between the central and state governments is a feature of a federal state, and this is correct.

Option 2 states that a federal state has an unwritten constitution. However, this is incorrect. A federal state can have either a written or unwritten constitution. The presence or absence of a written constitution does not determine whether a country is federal or not.

Therefore, the correct answer is option 1. Alert - correct answer should be option 3, as both statements 1 and 2 are incorrect.