In the following compounds, the decreasing order of basic strength will be

Options

A. `(C_2H_5)_2NHgtNH_3gtC_2H_5NH_2`
B. `NH_3gtC_2H_5NH_2gt(C_2H_5)_2NH`
C. `(C_2H_5)_2NHgtC_2H_5NH_2gtNH_3`
D. `C_2H_5NH_2gtNH_3gt(C_2H_5)NH`

Explanation

To determine the decreasing order of basic strength among the given compounds (secondary amine, primary amine, and ammonia), we can analyze the effect of alkyl groups on the basicity of amines. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
We have three types of compounds:
1. Secondary amine (R2NH)
2. Primary amine (RNH2)
3. Ammonia (NH3)

### Step 2: Understand Basicity
Basicity in amines is largely influenced by the availability of the lone pair of electrons on the nitrogen atom. The more electron density on the nitrogen, the stronger the base.

### Step 3: Analyze the Secondary Amine
In a secondary amine, there are two alkyl groups attached to the nitrogen. Alkyl groups are electron-donating due to their +I (inductive) effect, which increases the electron density on the nitrogen atom. This makes the lone pair of electrons more available for protonation, thus increasing the basicity.

### Step 4: Analyze the Primary Amine
In a primary amine, there is only one alkyl group attached to the nitrogen. While this group also exerts a +I effect, it does not increase the electron density as much as in the secondary amine because there is only one alkyl group. Therefore, the basicity of the primary amine is less than that of the secondary amine.

### Step 5: Analyze Ammonia
Ammonia (NH3) has no alkyl groups attached to the nitrogen. Consequently, it lacks the +I effect that increases electron density. While ammonia is still basic due to the presence of a lone pair of electrons, it is the weakest base among the three compounds because it does not benefit from any electron-donating groups.

### Step 6: Establish the Order of Basic Strength
Based on the analysis:
- Secondary amine has the highest basic strength due to the presence of two alkyl groups.
- Primary amine has moderate basic strength due to one alkyl group.
- Ammonia has the lowest basic strength as it has no alkyl groups.

Thus, the decreasing order of basic strength is:
**Secondary amine > Primary amine > Ammonia**

### Final Answer
The correct order of decreasing basic strength is:
**Secondary Amine > Primary Amine > Ammonia**

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