In an electrostatic field, the combination of subatomic particles that would attract to one another is D) proton and electron.
Protons have a positive charge, while electrons have a negative charge. Opposite charges attract each other, so protons and electrons attract.
The other combinations are as follows:
- A) electron and neutron: Neutrons are neutral and do not experience electrostatic attraction to charged particles.
- B) proton and neutron: Neutrons are also neutral, so there is no electrostatic attraction between them.
- C) electron and electron: Like charges repel each other, so electrons would not attract.
Therefore, the correct answer is D) proton and electron.