Which of the following acids is used in eye wash? 

Boric acid 

The correct answer is option 4. Boric acid.

Boric acid is a mild antiseptic with mild antibacterial and antifungal properties, making it suitable for various medicinal and ophthalmic applications, including eyewash solutions.

Here is why boric acid is used in eye wash:

1. Mild Antiseptic Properties: Boric acid has mild antiseptic properties, which means it can help prevent bacterial and fungal infections. When used in eye wash solutions, it can assist in cleansing and soothing the eyes.

2. Buffering Agent:  Boric acid can act as a buffering agent, helping to maintain the pH of the eye wash solution. The eye has a delicate pH balance, and maintaining this balance is essential for comfort and eye health.

3. Gentle on Eyes: Boric acid is generally considered to be gentle on the eyes, and solutions containing boric acid are often used to irrigate the eyes or clean them in case of irritation or minor injuries.

4. Preservative: Boric acid can also act as a preservative in eye wash solutions, helping to prevent the growth of microorganisms within the solution.

It's important to note that any eyewash solution, including those containing boric acid, should be used according to specific guidelines and recommendations. If someone has an eye condition, irritation, or an eye infection, it's advisable to consult with a healthcare professional for appropriate diagnosis and treatment.