Which of the following form tetrahydridoborates

Options

A. `(Li)`
B. `Na`
C. `NH_(4)^(+)`
D. `Ag^(+)`

Explanation

To determine which of the given ions form tetrahydridoborates, we need to analyze each option based on their ability to form stable complexes with the tetrahydroborate ion (BH4^-).

### Step-by-Step Solution:

1. **Identify the Compounds:**
We have four options:
- Lithium (Li^+)
- Sodium (Na^+)
- Ammonium (NH4^+)
- Silver (Ag^+)

2. **Examine Lithium (Li^+):**
- Lithium can form tetrahydridoborate, which is known as lithium tetrahydridoborate (LiBH4).
- This compound is stable and commonly used in various chemical reactions.

3. **Examine Sodium (Na^+):**
- Sodium can also form tetrahydridoborate, known as sodium tetrahydridoborate (NaBH4).
- Similar to lithium, this compound is stable and widely utilized, especially as a reducing agent.

4. **Examine Ammonium (NH4^+):**
- Ammonium ion does not have available electrons for donation to form a stable tetrahydridoborate.
- Therefore, ammonium does not form tetrahydridoborate.

5. **Examine Silver (Ag^+):**
- Silver ion reacts with hydride ions and reduces them rather than forming a stable tetrahydridoborate.
- Thus, silver does not form tetrahydridoborate either.

6. **Conclusion:**
- The ions that can form tetrahydridoborates are lithium (Li^+) and sodium (Na^+).
- Therefore, the correct answer is that lithium and sodium form tetrahydridoborates.

### Final Answer:
Lithium (Li^+) and Sodium (Na^+) form tetrahydridoborates.