The lowest molecular mass monocarboxylic acid containing a secondary carbon atom is ..........

Explanation

To find the lowest molecular mass monocarboxylic acid containing a secondary carbon atom, we can follow these steps:

### Step 1: Understand the structure of a secondary carbon
A secondary carbon atom is one that is bonded to two other carbon atoms. In the case of carboxylic acids, we need to identify a structure where the carboxylic acid group (-COOH) is attached to a secondary carbon.

### Step 2: Identify the simplest structure
The simplest structure that contains a secondary carbon and a carboxylic acid group is 2-propanol (isopropyl) with a carboxylic acid group. The structure can be represented as follows:
- The secondary carbon is in the middle, connected to two methyl groups (CH3).
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