How many of the following is/are not optically active amine?
(I) `CH_3NH_2`
(II) `CH_3 NHCH_3`
(III) `CH_3CH_2CH_2N(CH_3)C_2H_5`
(IV) Secondary butylamine

Explanation

To determine how many of the given amines are not optically active, we need to analyze each compound for the presence of a chiral center. A chiral center is typically a carbon atom bonded to four different groups. In the case of amines, a nitrogen atom can also serve as a chiral center if it is bonded to three different groups and has a lone pair.

Let's analyze each compound step by step:

### Step 1: Analyze `CH3NH2` (Methylamine)
- Structure: `CH3-NH2`
- The nitrogen atom is bonded to:
- One methyl group (`CH3`)
...