Amongst the following, the maximum number of antacids is : valium, meprobamate, ranitidine, phenelzine, cimetidine, omeprazole, penicillin, chloramphenicol, chlorpheniramine.

Explanation

To determine which of the given options contains the maximum number of antacids, we need to identify which of the listed substances are classified as antacids.

### Step-by-Step Solution:

1. **Understanding Antacids**: Antacids are substances that neutralize stomach acidity. They are commonly used to relieve heartburn, indigestion, and upset stomach.

2. **Analyzing the Options**:
- **Valium**: This is a brand name for diazepam, which is a benzodiazepine used primarily for anxiety and muscle spasms. It is not an antacid.
- **Meprobamate**: This is an anxiolytic medication, not an antacid.
- **Ranitidine**: This is a histamine H2-receptor antagonist that reduces stomach acid production. It is used to treat ulcers and gastroesophageal reflux disease (GERD), but it is not classified as a traditional antacid.
- **Phenelzine**: This is a monoamine oxidase inhibitor (MAOI) used to treat depression. It is not an antacid.
- **Cimetidine**: This is also a histamine H2-receptor antagonist similar to ranitidine, used to reduce stomach acid. It is not a traditional antacid.
- **Omeprazole**: This is a proton pump inhibitor (PPI) that decreases the amount of acid produced in the stomach. It is not a traditional antacid.
- **Penicillin**: This is an antibiotic and has no antacid properties.
- **Chloramphenicol**: This is an antibiotic used to treat bacterial infections. It is not an antacid.
- **Chlorpheniramine**: This is an antihistamine used to relieve allergy symptoms. It is not an antacid.

3. **Identifying Antacids**: From the analysis, the substances that are related to reducing stomach acidity are:
- Ranitidine
- Cimetidine
- Omeprazole

4. **Conclusion**: Among the options provided, the substances that can be considered as having antacid properties are Ranitidine, Cimetidine, and Omeprazole. Therefore, the maximum number of antacids in the list is **three**.

### Final Answer:
The maximum number of antacids among the given options is **three** (Ranitidine, Cimetidine, and Omeprazole).