Define an acid in terms of ions.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Concept of Acids:**
- Acids are substances that can be defined based on their ability to interact with ions, particularly hydrogen ions.

2. **Identifying Key Characteristics:**
- An acid must contain hydrogen (H) in its molecular structure.
- It must be capable of donating a proton (H⁺ ion) to another substance.
...