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.