Introduction:
When two protons move parallel to each other, they experience both electric and magnetic forces of interaction. The ratio of these forces can be determined by considering their magnitudes.

Electric Force:
The electric force between two charged particles is given by Coulomb's law: F_e = k * (q1 * q2) / r^2, where F_e is the electric force, k is the electrostatic constant (9 × 10^9 N m^2/C^2), q1 and q2 are the charges of the particles, and r is the distance between them.

Magnetic Force:
The magnetic force experienced by a charged particle moving with velocity V in a magnetic field B is given by F_m = q * (V x B), where F_m is the magnetic force, q is the charge of the particle, V is the velocity vector, and B is the magnetic field vector.

Parallel Motion:
In the given scenario, the protons are moving parallel to each other with the same velocity V. As a result, the magnetic force experienced by each proton is perpendicular to their relative velocity, and hence, perpendicular to each other. This implies that the magnetic forces do not contribute to the net force between the protons.

Ratio of Forces:
To find the ratio of the electric and magnetic forces, we only need to consider the electric force between the protons.

Let's assume the distance between the protons is r, and each proton has a charge of q.

The electric force between them is given by F_e = k * (q * q) / r^2 = k * q^2 / r^2.

Since the magnetic force is not contributing to the net force, the ratio of the electric force to the magnetic force is:

F_e / F_m = (k * q^2 / r^2) / 0 = ∞.

Conclusion:
In the given scenario, where two protons move parallel to each other with the same velocity, the ratio of the electric force to the magnetic force of interaction between them is infinite. This implies that the electric force dominates the interaction between the protons, while the magnetic force has no effect.