B

Step 1: Understand that ionization energy (i) refers to the energy required to remove an electron from an atom. In this case, we want to determine which of the following particles is most effective at ionizing a hydrogen atom: an electron, a hydrogen ion, or a helium ion.

Step 2: Analyze the particles:
- **Electron**: An incoming electron will not effectively ionize the hydrogen atom unless it has sufficient energy (greater than W i) to overcome the ionization energy of the hydrogen atom. Thus, its efficacy depends on kinetic energy.
- **Hydrogen ion (H⁺)**: A hydrogen ion has lost its electron and has a positive charge. When it approaches a neutral hydrogen atom, it experiences a strong electrostatic attraction due to its positive charge and can effectively ionize the hydrogen atom by pulling its electron away.
- **Helium ion (He⁺)**: A helium ion has two protons and one electron. Thus, it is also positively charged and can effectively ionize a hydrogen atom through its strong positive charge, similar to H⁺. However, due to the greater charge (+2), it has a stronger electrostatic force of attraction compared to H⁺. Thus, while both ions could ionize hydrogen, the helium ion has a stronger effect due to higher charge.

Step 3: Conclusion: The helium ion is more effective than both the hydrogen ion and the incoming electron. Therefore, the answer is the helium ion.

Therefore, the correct answer is B (helium ion).