B

Step 1: Understand the concept of stationary waves. In stationary waves (or standing waves), certain points called nodes have specific characteristics.
Step 2: At nodes, the amplitude of the wave is zero, meaning that there is no displacement of the medium.
Step 3: Since there is no displacement at the nodes, the changes in pressure and density of the medium are at their minimum because the particles at the nodes are not moving.
Step 4: Therefore, the correct answer is that at nodes, the change in pressure and density are minimum.
Conclusion: Thus, the correct answer is Option B.