To determine which of the three species, \( \text{Na}^+, \text{Ne}, \text{F}^- \), is the largest in size, we can follow these steps:
### Step 1: Identify the number of electrons
All three species are isoelectronic, meaning they have the same number of electrons. Each species has 10 electrons:
- \( \text{Na}^+ \) has 10 electrons (it loses one electron from sodium, which has 11 electrons).
- \( \text{Ne} \) has 10 electrons (it is a neutral atom).
- \( \text{F}^- \) has 10 electrons (it gains one electron to become negatively charged).
### Step 2: Identify the number of protons
Next, we need to determine the number of protons in each species:
- \( \text{Na}^+ \): Sodium has an atomic number of 11, so it has 11 protons.
- \( \text{Ne} \): Neon has an atomic number of 10, so it has 10 protons.
- \( \text{F}^- \): Fluorine has an atomic number of 9, so it has 9 protons.
### Step 3: Analyze the attraction between protons and electrons
The size of an atom or ion is influenced by the attraction between the protons in the nucleus and the electrons surrounding it. The more protons there are, the stronger the attraction to the electrons:
- \( \text{Na}^+ \) has 11 protons attracting 10 electrons, resulting in a strong attraction and a smaller size.
- \( \text{Ne} \) has 10 protons attracting 10 electrons, resulting in a balanced attraction and a moderate size.
- \( \text{F}^- \) has 9 protons attracting 10 electrons, resulting in a weaker attraction and a larger size due to increased electron-electron repulsion.
### Step 4: Compare sizes based on proton-electron ratio
Since \( \text{F}^- \) has the least number of protons (9) compared to its electrons (10), it will have the weakest attraction, leading to a larger size. In contrast, \( \text{Na}^+ \) has the strongest attraction due to having the most protons (11) for the same number of electrons, making it the smallest.
### Conclusion
Based on the analysis, the order of size from largest to smallest is:
1. \( \text{F}^- \) (largest)
2. \( \text{Ne} \) (medium)
3. \( \text{Na}^+ \) (smallest)
Thus, the largest in size out of \( \text{Na}^+, \text{Ne}, \text{F}^- \) is \( \text{F}^- \).
### Final Answer
The largest in size is \( \text{F}^- \).
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