A block with a mass of 20 kg moves towards the east at a constant velocity across a rough horizontal surface, as shown in the diagram below - NSC Technical Sciences - Question 1 - 2022 - Paper 1

Since the block moves at a constant velocity, the net force acting on it must be zero according to Newton's first law. This implies that the applied force ($F_{app}$) must exactly balance the frictional force ($F_r$) acting against the motion. Therefore, the correct answer is B) $F_{app} < F_r$ and $a = 0 ext{ m/s}^2$.