Let's carefully analyze the given chemical equation:
[tex]\[ \text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl} \][/tex]
In this equation, a sodium ion ([tex]\(\text{Na}^+\)[/tex]) reacts with a chloride ion ([tex]\(\text{Cl}^-\)[/tex]) to form one formula unit of sodium chloride ([tex]\(\text{NaCl}\)[/tex]).
To determine which statement best describes the relationship between the substances in the equation, let's look at each option in detail:
1. The number of sodium ions is equal to the number of formula units of salt.
- Each sodium ion ([tex]\(\text{Na}^+\)[/tex]) pairs with exactly one chloride ion ([tex]\(\text{Cl}^-\)[/tex]) to form one formula unit of sodium chloride ([tex]\(\text{NaCl}\)[/tex]). Therefore, for every sodium ion, there is one corresponding formula unit of NaCl.
- This statement is accurate.
2. The number of sodium ions is less than the number of chloride ions.
- According to the equation, each sodium ion reacts with one chloride ion. This means the number of sodium ions is equal to the number of chloride ions, not less.
- This statement is incorrect.
3. The number of chloride ions is less than the number of formula units of salt.
- Again, since each chloride ion pairs with one sodium ion to form one formula unit of NaCl, the number of chloride ions cannot be less than the number of formula units of salt.
- This statement is incorrect.
4. The number of sodium ions is two times the number of formula units of salt.
- Given that each sodium ion pairs with one chloride ion to form one formula unit of NaCl, the number of sodium ions cannot be twice the number of formula units of salt.
- This statement is incorrect.
Based on the detailed analysis, the best statement that describes the relationship between the substances in the given chemical equation is:
The number of sodium ions is equal to the number of formula units of salt.
Therefore, the correct answer is:
```
1
```
