Given that interionic distance in `Na^(+), F^(-)` crystal is `2.31 Å and r_(F^(+)) = 1.36 Å`, which of the following predictions will be right

Options

A. `r_(Na^(+))//r_(F^(-)) ~~ 0.7`
B. coordination number of `Na^(+)` = coordinatin number of `F^(-) = 6`
C. `Na^(+), F^(-)` will have rock salt type crystal structure
D. effective nuclear charge for `Na^(+) and F^(-)` are equal

Explanation

To solve the problem, we need to analyze the given information about the Na⁺ and F⁻ ions in the crystal structure of sodium fluoride (NaF). We will evaluate the statements provided in the question based on the properties of ionic compounds and their structures.

### Step-by-Step Solution:

1. **Understanding the Ionic Radii and Interionic Distance**:
- The interionic distance (d) in Na⁺ and F⁻ crystal is given as 2.31 Å.
- The radius of F⁻ (r_F⁻) is given as 1.36 Å.
- We can find the radius of Na⁺ (r_Na⁺) using the relation:
\[ d = r_{Na^+} + r_{F^-} \]
- Rearranging gives:
\[ r_{Na^+} = d - r_{F^-} = 2.31 \, \text{Å} - 1.36 \, \text{Å} = 0.95 \, \text{Å} \]

2. **Calculating the Radius Ratio**:
- Now, we can calculate the radius ratio \( \frac{r_{Na^+}}{r_{F^-}} \):
\[ \frac{r_{Na^+}}{r_{F^-}} = \frac{0.95 \, \text{Å}}{1.36 \, \text{Å}} \approx 0.70 \]
- This confirms that the first statement about the radius ratio being nearly equal to 0.7 is correct.

3. **Coordination Number**:
- In the rock salt structure (NaCl type), both Na⁺ and F⁻ have a coordination number of 6. This means each ion is surrounded by 6 oppositely charged ions.
- Therefore, the second statement regarding the coordination number of Na⁺ and F⁻ being 6 is true.

4. **Structure Type**:
- The structure of NaF is indeed similar to that of NaCl, which is a rock salt structure. Hence, the third statement is also true.

5. **Effective Nuclear Charge**:
- The effective nuclear charge (Z_eff) is not the same for Na⁺ and F⁻, even though they are isoelectronic (having the same number of electrons).
- Na⁺ has 11 protons, while F⁻ has 9 protons. Therefore, the effective nuclear charges will differ due to the different number of protons in the nucleus.
- Thus, the fourth statement about the effective nuclear charge of Na⁺ and F⁻ being equal is false.

### Conclusion:
- The correct statements are:
1. \( \frac{r_{Na^+}}{r_{F^-}} \approx 0.7 \) (True)
2. Coordination number of Na⁺ and F⁻ is 6 (True)
3. NaF has a rock salt type of structure (True)
4. Effective nuclear charge of Na⁺ and F⁻ are equal (False)

### Final Answer:
The predictions that are right are statements 1, 2, and 3.

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