Which is a dimensionless quantity ?

Dimensionless quantity is

Dimensionless quantity is

It can be shown that probability p(r) that the electron in the ground state of the hydrogen atom will be detected inside a sphere of radius R is given by p(r)=1-e^(-2x)(1+2x+2x^(2)) . in which x, a dimensionless quantity, is equal to r//a . Find r for p(r)=0.90 .

Which of the following is a dimensionless quantity?

Which of the following is not a dimensionless quantity ?

A : Displacement gradient is a dimensionless quantity. R : Displacement is dimensionless quantity.