B

Step 1: Analyze the forces. Since the three forces are represented by the sides of a triangle, they are in equilibrium.
Step 2: The resultant force acting on the particle is zero, indicating that the particle's state of motion will not change.
Step 3: According to Newton's First Law of Motion, a particle will continue in its state of rest or uniform motion unless acted upon by a net force.
Therefore, the velocity of the particle will remain unchanged in both magnitude and direction.
Thus, the correct answer is B.