Number of base SI units is

The correct answer is Option 7.

To understand why the number of base SI units is 7, let us look at the International System of Units (SI). The SI system is built upon a foundation of seven mutually independent base units, from which all other measurement units (derived units) are established.

These seven fundamental physical quantities and their corresponding SI base units are:
1. Length: meter (m)
2. Mass: kilogram (kg)
3. Time: second (s)
4. Electric Current: ampere (A)
5. Thermodynamic Temperature: kelvin (K)
6. Amount of Substance: mole (mol)
7. Luminous Intensity: candela (cd)

Since there are exactly 7 base quantities defined in the SI system, the number of base SI units is 7.