Explanation:
In SI units, a unit of charge is called Coulomb. Here is an explanation of why Coulomb is the correct unit of charge.

1. Charge:
Charge is a fundamental property of matter that can be positive or negative. It is the property responsible for electromagnetic interactions. The charge of an object determines its behavior in an electric field.

2. Coulomb:
Coulomb is the SI unit of electric charge. It is named after the French physicist Charles-Augustin de Coulomb, who made significant contributions to the field of electromagnetism. One coulomb (C) is defined as the amount of charge transported by a current of one ampere (A) in one second.

3. Ampere:
Ampere is the SI unit of electric current. It is named after the French physicist André-Marie Ampère, who made fundamental contributions to the understanding of electromagnetism. One ampere is defined as the flow of one coulomb of charge per second.

4. Relationship between Coulomb and Ampere:
The relationship between Coulomb and Ampere can be understood by the definition of current. Current is the rate of flow of charge. Therefore, if one ampere of current flows for one second, it means that one coulomb of charge has passed through a point in the circuit.

5. Other units of charge:
While Coulomb is the standard unit of charge in SI, there are other units used in different systems of measurement. For example, the milliampere-hour (mAh) is often used to measure the charge capacity of batteries. However, when dealing with SI units and scientific calculations, it is important to use Coulomb as the unit of charge.

Conclusion:
In SI units, a unit of charge is called Coulomb. It is defined as the amount of charge transported by a current of one ampere in one second. Coulomb is the standard unit of charge and is used in scientific calculations and measurements.