A

Step 1: Understand the concept of spin in quantum mechanics.
Spin is a fundamental property of particles that describes their intrinsic angular momentum. Particles can have integral (integer) or half-integral (non-integer) spin values.

Step 2: Identify the types of particles in the options:
- Photon: A fundamental particle in quantum mechanics that possesses a spin of 1 (integral spin) and is a force carrier for electromagnetic force.
- Pion (π meson): A meson composed of a quark and an antiquark; it has an integer spin of 0 (boson).
- Proton: A baryon made of three quarks that has a spin of 1/2 (half-integral spin) and is a fermion.
- K-meson (kaon): A meson also composed of a quark and an antiquark with an integral spin of 0 (boson).

Step 3: Analyze the options based on the spin values:
The only particle in the provided options that possesses half-integral spin is the Proton, which has a spin of 1/2. Hence, the correct answer is:
Therefore, the correct answer is: C (Proton).