Chemistry Regents Practice Test 2025 – The All-in-One Guide to Exam Success!

The ion that has no electrons is the hydrogen ion, often represented as H+. When a hydrogen atom loses its single electron, it becomes a hydrogen ion, which means it is left with just one proton and no electrons. This results in a charged species with a +1 charge, indicating that it has lost its electron.

In contrast, the other ions mentioned retain some electrons. O2- indicates an oxygen atom that has gained two additional electrons, leading to a total of ten electrons (where it originally had eight). Na+ represents a sodium atom that has lost one electron, resulting in ten electrons, as sodium originally has eleven. Similarly, Cl- is a chloride ion that has gained one electron, giving it a total of eighteen electrons while originally having seventeen.

Thus, the hydrogen ion (H+) is unique in that it completely lacks electrons, making it the correct answer to the question regarding which ion has no electrons.