The compound 1- (N-ethyl-N-methyl)- propanamine forms non-superimposable mirror images . But this compound does not show optical activity because of the :

Options

A. Absence fo a chiral (N) atom
B. Prersence of chiral (N) atom
C. Presence of lone pair on (N) atom
D. Rapid filipping of one form into the another

Explanation

To solve the question regarding the optical activity of the compound 1-(N-ethyl-N-methyl)-propanamine, we will analyze the structure and the concept of chirality in detail.

### Step-by-Step Solution:

1. **Identify the Structure**:
- The compound 1-(N-ethyl-N-methyl)-propanamine consists of a propanamine backbone with an ethyl and a methyl group attached to the nitrogen atom.
- The structure can be represented as follows:
```
CH3-CH2-N(CH3)-CH2-CH3
```

2. **Determine Chirality**:
- A chiral center is typically a carbon atom bonded to four different substituents. However, in this case, the chiral center is the nitrogen atom.
- The nitrogen atom has three different substituents: an ethyl group (C2H5), a methyl group (CH3), and a propyl group (C3H7) along with a lone pair of electrons.

3. **Mirror Image Formation**:
- The compound can form non-superimposable mirror images due to the presence of the chiral nitrogen atom. This means that if you were to create a mirror image of the compound, it would not be possible to overlay the two structures perfectly.

4. **Optical Activity**:
- Generally, compounds that have non-superimposable mirror images are optically active. However, in this case, the compound does not exhibit optical activity.
- The reason for this is that the nitrogen atom can rapidly interconvert between its two configurations due to the presence of the lone pair of electrons. This rapid flipping or inversion prevents the compound from being stable in one specific chiral form.

5. **Conclusion**:
- Although the compound has a chiral nitrogen atom, the rapid interconversion between its mirror images means that it does not maintain a stable chiral configuration. Therefore, it does not exhibit optical activity.

### Final Answer:
The compound 1-(N-ethyl-N-methyl)-propanamine does not show optical activity despite forming non-superimposable mirror images because of the rapid flipping (inversion) of the nitrogen atom, which leads to interconversion between the two forms.