During circular motion about the origin, a particle's position...

The areal velocity of a particle is given by $\dfrac{dA}{dt} = \dfrac{1}{2} r^2 \omega$.

Since the position vector sweeps out equal areas in equal intervals of time, the areal velocity is constant.

For circular motion about the origin, the radius $r$ is constant. Therefore, the angular velocity $\omega$ must also be constant.

The speed of the particle is $v = r\omega$. Since both $r$ and $\omega$ are constant, the speed $v$ remains constant.

Because the speed is constant, the tangential acceleration is $a_t = \dfrac{dv}{dt} = 0$. Since it is zero, it remains constant.

The direction of motion changes continuously, meaning the velocity vector is not constant.

The total acceleration is purely centripetal ($a_c = r\omega^2$) and its direction continuously changes as it always points towards the origin. Thus, the acceleration vector is not constant.