Out of the following acid base-reactions, reaction (b) and (c) are possible.
a. `PH_(3) + overset(o+)NH_(4) rarr overset(o+)PH_(4) +NH_(3)`
b. `NH_(3) + Poverset(o+)H_(4) rarr Noverset(o+)H_(4) + PH_(3)`
c. `(CH_(3))_(3) P + overset(o+)NH_(4) rarr (CH_(3))_(3) overset(o+)PH + NH_(3)`
d. `(CH_(3))_(3) N + PH_(4)^(o+) rarr (CH_(3))_(2) overset(o+)NH + PH_(3)`

Explanation

To determine which of the given acid-base reactions are possible, we need to analyze each reaction based on the concept of proton affinity and the relative strengths of the acids and bases involved.

### Step-by-Step Solution:

1. **Analyze Reaction (a):**
- Reaction: \( PH_3 + NH_4^+ \rightarrow PH_4^+ + NH_3 \)
- Here, \( NH_4^+ \) is a stronger acid than \( PH_3 \) because \( NH_4^+ \) can donate a proton more readily.
- \( NH_3 \) is a stronger base than \( PH_3 \) because it can accept a proton more readily.
- Therefore, this reaction is **not feasible** because \( PH_3 \) cannot act as a base against \( NH_4^+ \).

2. **Analyze Reaction (b):**
- Reaction: \( NH_3 + PH_4^+ \rightarrow NH_4^+ + PH_3 \)
- In this case, \( PH_4^+ \) is a stronger acid than \( NH_3 \).
- \( NH_3 \) can accept a proton from \( PH_4^+ \) to form \( NH_4^+ \) and \( PH_3 \).
- Therefore, this reaction is **feasible**.

3. **Analyze Reaction (c):**
- Reaction: \( (CH_3)_3P + NH_4^+ \rightarrow (CH_3)_3PH + NH_3 \)
- Here, \( NH_4^+ \) is again a strong acid, and \( (CH_3)_3P \) can accept a proton to form \( (CH_3)_3PH \).
- Since \( (CH_3)_3P \) has a lower proton affinity compared to \( NH_3 \), this reaction is also **feasible**.

4. **Analyze Reaction (d):**
- Reaction: \( (CH_3)_3N + PH_4^+ \rightarrow (CH_3)_2NH + PH_3 \)
- In this case, \( PH_4^+ \) is a stronger acid than \( (CH_3)_3N \).
- However, \( (CH_3)_3N \) cannot accept a proton from \( PH_4^+ \) because it has a higher proton affinity than \( PH_3 \).
- Therefore, this reaction is **not feasible**.

### Conclusion:
Based on the analysis:
- Reaction (a) is not feasible.
- Reaction (b) is feasible.
- Reaction (c) is feasible.
- Reaction (d) is not feasible.

Thus, the statement that reactions (b) and (c) are possible is **true**.