A hydrogen atom which has lost an electron contains

Analysis

To solve this, we need to look at the atomic structure of a neutral hydrogen atom and understand what happens when it becomes an ion.

Concept: Atomic Structure of Hydrogen

1. Neutral Hydrogen ($^1_1H$): A standard hydrogen atom consists of 1 proton in the nucleus and 1 electron orbiting the nucleus. Notably, the most common isotope of hydrogen (Protium) contains zero neutrons.
2. Ionization: When an atom "loses an electron," it becomes a positively charged ion (a cation). In the case of hydrogen, if it loses its only electron, it is left with only its nucleus.

Step-by-Step Solution

• Step 1: Identify the components of a neutral hydrogen atom: 1 proton, 0 neutrons, and 1 electron.
• Step 2: Apply the change described in the question: The atom loses its 1 electron.
• Step 3: Calculate the remaining particles: • Protons: 1 (remains unchanged) • Electrons: 1 - 1 = 0 • Neutrons: 0 (remains unchanged)
• Step 4: Conclusion: After losing its electron, the hydrogen atom is left with only the 1 proton that constitutes its nucleus. This is effectively a hydrogen ion ($H^+$).

Identifying the Answer

Comparing our result to the options provided:

• A. one proton only — Matches our finding.
• B. one neutron only — Incorrect (Hydrogen has no neutrons).
• C. one proton and one neutron — Incorrect (Hydrogen has no neutrons).
• D. one proton, one electron and one neutron — Incorrect (This describes a different element or isotope).

Exam Tip

Always remember the "Hydrogen Exception": Hydrogen is the only element in the periodic table that typically has no neutrons in its nucleus. When you see questions about hydrogen, keep in mind that its mass number (1) is equal to its atomic number (1), confirming the absence of neutrons ($Mass = Protons + Neutrons \rightarrow 1 = 1 + 0$).