| Answer | Crossword Clue |
|---|---|
| ATOM | Proton plus electron. |
| ATOM | Proton and electron. |
| PARTICLE | Proton or electron |
| PARTICLE | Proton or electron, take your pick |
| muonium | electron and a positively charged muon bound together by electrical attraction in the same manner as the electron and proton in a hydrogen atom |
| muoniums | electron and a positively charged muon bound together by electrical attraction in the same manner as the electron and proton in a hydrogen atom |
