Alright — let's do this. The question asks which statement is not true about a wave in a plucked string. Let's analyze each option: A) It has a crest: A wave on a plucked string is a transverse wave, which is characterized by crests (points of maximum displacement above the equilibrium position) and troughs (points of maximum displacement below the equilibrium position). So, this statement is true. B) It is transverse: In a transverse wave, the particles of the medium oscillate perpendicular to the direction of wave propagation. When a string is plucked, the string particles move up and down, while the wave travels along the length of the string. This is the definition of a transverse wave. So, this statement is true. C) It is longitudinal: In a longitudinal wave, the particles of the medium oscillate parallel to the direction of wave propagation (e.g., sound waves). Waves on a plucked string do not exhibit this type of particle motion. So, this statement is false. D) It is mechanical: A mechanical wave requires a medium to propagate and involves the transfer of energy through the vibration of particles in that medium. A wave on a plucked string requires the string itself as a medium. So, this statement is true. Since the question asks for the statement that is not true, the correct option is C. The final answer is $\boxed{\text{C) It is longitudinal}}$. What's next?