Are readians and streadians the basic unit of si justify your answer?

Answer 1

It seems that some people consider these base units, some don't. You might want to make up your own mind about what you think about this point. However, I would go for "derived unit", simply because that's the official definition.

A radian is used to measure angles; the way it is defined is by dividing an arc on a circle by the radius; so naturally, the units are meters/meters. Or substitute any other unit of length for meter, such as angstrom/angstrom or AU/AU or light-years/light-years; but the result would be exactly the same. In other words, it's a dimensionless unit.

The same applies to the steradian, which is radian2. This, of course, is also a dimensionless unit. It is also officially considered a derived unit.

Answer 2

No, radians and steradians are not basic units of the SI system. They are supplementary units used to measure angles and solid angles, but they are derived from the basic SI units such as meters, kilograms, and seconds. Radians are derived from the arc length of a circle, while steradians are derived from the surface area of a sphere.