Write increasing order of basic strength of following:
`(a)CH_(3) -underset(O)underset(||)C - overset(..)NH_(2)" "(b) CH_(3) - CH_(2) - overset(..)NH_(2)`
`(c)CH_(3) - underset(..)underset(NH)underset(||)C - overset(..)NH_(2)" "(d)NH_(2) - underset(..)underset(NH) underset(||)C - overset(..)NH_(2)`

Answer

To determine the increasing order of basic strength for the given compounds, we need to analyze the influence of the functional groups and the presence of lone pairs on the nitrogen atoms in each compound. Basic strength is influenced by the availability of lone pairs for donation, as well as the presence of electron-withdrawing or electron-donating groups that can affect the stability of the lone pairs.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- (a) CH₃CO-NH₂ (Acetamide)
- (b) CH₃-CH₂-NH₂ (Ethylamine)
- (c) CH₃-NH-C(=NH)-NH₂ (Aminoguanidine)
- (d) NH₂-C(=NH)-NH₂ (Guanidine)

2. **Analyze Compound (a) CH₃CO-NH₂:**
- The lone pair on the nitrogen atom is involved in resonance with the carbonyl group (C=O), which is an electron-withdrawing group. This delocalization reduces the availability of the lone pair for protonation, making it less basic.

3. **Analyze Compound (b) CH₃-CH₂-NH₂:**
- Ethylamine has no electron-withdrawing groups nearby. The lone pair on the nitrogen is readily available for donation, making it more basic than acetamide.

4. **Analyze Compound (c) CH₃-NH-C(=NH)-NH₂:**
- This compound has two NH₂ groups and one NH group. The presence of multiple nitrogen atoms increases the number of available lone pairs. However, the NH group can also engage in resonance, but it is less effective than the resonance in acetamide. Thus, it is more basic than acetamide but less than ethylamine.

5. **Analyze Compound (d) NH₂-C(=NH)-NH₂:**
- Guanidine has three nitrogen atoms, all of which have lone pairs. The structure allows for resonance stabilization, but the availability of three lone pairs makes it the most basic among the four compounds.

6. **Order the Basic Strength:**
- Based on the analysis:
- (a) CH₃CO-NH₂ < (c) CH₃-NH-C(=NH)-NH₂ < (b) CH₃-CH₂-NH₂ < (d) NH₂-C(=NH)-NH₂

### Final Answer:
The increasing order of basic strength is:
(a) < (c) < (b) < (d)