Final answer:
The principal resources of an Institutional Unit are economic resources, such as oil, natural gas, and minerals. In the example of Iran, oil and natural gas are pivotal to the economy, along with a wide range of other minerals and resources from the Caspian Sea.
Step-by-step explanation:
The principal resources of an Institutional Unit (IU) can vary depending on the context and the type of unit being considered. However, in the context of a country's economy, the principal resources refer to material or economic resources that are utilized for production and economic activities. Iran, as an example, possesses a variety of such resources including oil and natural gas reserves, which substantially contribute to its national income. The Caspian Sea not only offers a fishing industry but also contains oil reserves beneath its seabed. Asides from hydrocarbons, Iran's economy is also supported by mineral resources such as coal, copper, lead, molybdenum, phosphates, rare earth elements, uranium, and many more, which add to the diversity of the economy. While oil and gas remain dominant in the revenue stream, Iran is working toward diversifying its economy with its growing manufacturing sector.