Fill in the blank by choosing the appropriate word/words from those given in the brackets.
(acetaldehyde, formaldehyde, benzaldehyde, yellow, white, violet, Cannizzaro's, Liebermann, no `alpha`-hydrogen atom, `1alpha`-hydrogen atom, `2alpha`-hydrogen atoms, aldol, `beta`-hydroxy aldehyde, aldol condensation, mixed condensation, + I,-I, -M,+ M. decreases, increases, benzalchloride, PCI, SOCh. sec, alcohol, tert, alcohol, phenylhydrozone, semicarbazone, more, less, acetals, ketals, silver mirror, test, urotropine, acetaldehyde cyanohydrin, lactic acid, benzoic acid, Sodalime, ethanoic acid, propanoic acid, electrolysis, Kolbe's electrolytic reaction, carbon dioxide, water, amides, alpha, halogen, phosphorus, weaker, stronger, ethyl alcohol, dibasic,monobasic, 2,2-dimethylpropanoic acid, `CH_(3)COCI`, acetic acid, `CH_(3)CH_(2)CH_(2)COOK`, enatiomers, diastereo, `K_(a)` `pk_(a)`, methanoic acid, higher, lower.)
The most common monocarboxylic acid contains two carbon atoms and may be represented by the structural formula ........

Explanation

To solve the question, we need to identify the most common monocarboxylic acid that contains two carbon atoms. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Monocarboxylic Acid
Monocarboxylic acids are organic acids that contain one carboxyl group (-COOH). The question specifies that we need to find one with two carbon atoms.

### Step 2: List Common Monocarboxylic Acids
The common monocarboxylic acids include:
- Formic acid (1 carbon)
...