A small block is moving on a frictionless horizontal circular track...

For a block moving on a circular track with a steady speed, the magnitude of velocity remains constant but its direction changes continuously.

Since velocity $\vec{v}$ is a vector, the continuous change in direction means the velocity is variable.

Linear momentum is given by $\vec{p} = m\vec{v}$. Since velocity is variable, linear momentum is also variable.

The block experiences a centripetal acceleration $\vec{a}$ directed towards the center of the circular track. As the block moves, the direction of this acceleration continuously changes, making the acceleration variable.

Kinetic energy is given by $K = \dfrac{1}{2}mv^2$. Since speed $v$ is constant and kinetic energy is a scalar quantity, it remains constant.

Centripetal force $\vec{F} = m\vec{a}$ also changes direction continuously, so it is a variable force.

Therefore, the block possesses variable linear momentum and variable acceleration.

Answer: Variable linear momentum and variable acceleration