The correct answer is option 'B': Nominal exchange rate.

Explanation:
Exchange rates refer to the value of one currency in terms of another currency. They are used to determine the relative value of different currencies in international trade and investment. Exchange rates fluctuate constantly due to various factors such as supply and demand, interest rates, inflation, and government policies.

There are two types of exchange rates:
1. Nominal Exchange Rate: The nominal exchange rate is the rate at which one currency can be exchanged for another currency. It represents the current market value of one currency in terms of another. For example, if the nominal exchange rate between the US dollar and the euro is 1.20, it means that 1 US dollar can be exchanged for 1.20 euros.

2. Real Exchange Rate: The real exchange rate takes into account the differences in inflation rates between two countries. It is calculated by adjusting the nominal exchange rate for the relative price levels of the two countries. The real exchange rate reflects the purchasing power of a currency in terms of another currency. It is used to compare the cost of goods and services between countries.

The real exchange rate is influenced by factors such as inflation differentials, productivity levels, terms of trade, and non-tradable goods. It is an important indicator of a country's competitiveness in international trade. A higher real exchange rate indicates a relatively higher cost of goods and services in a country compared to its trading partners, making its exports more expensive and imports cheaper.

In summary, exchange rates for one currency against another currency are known as nominal exchange rates. Real exchange rates, on the other hand, take into account differences in inflation rates and reflect the purchasing power of a currency. Both nominal and real exchange rates play a crucial role in international trade and investment.