Final answer:
The missing particle in the given reaction is the alpha particle.
Step-by-step explanation:
The missing particle in the given reaction is the alpha particle, represented by option A. Alpha particles are high-energy helium nuclei consisting of two protons and two neutrons. In the reaction, ¹² v6 C (carbon) combines with¹ v1 H (hydrogen) to form ¹³ v7 N (nitrogen) and the alpha particle.