**Core Concept**
Bleaching powder, also known as calcium hypochlorite, is a widely used disinfectant and antiseptic. Its antiseptic properties are attributed to its ability to release hypochlorous acid, a potent antimicrobial agent.

**Why the Correct Answer is Right**
The antiseptic property of bleaching powder is primarily due to the release of hypochlorous acid (HOCl) when it comes into contact with water. Hypochlorous acid is a strong oxidizing agent that disrupts the cellular membrane of microorganisms, ultimately leading to their death. The mechanism of action involves the formation of reactive oxygen species, which damage the microbial cell membrane and inhibit essential cellular processes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the antiseptic property of bleaching powder is not primarily due to its alkalinity.
**Option B:** This option is incorrect because the antiseptic property of bleaching powder is not primarily due to its ability to dehydrate microorganisms.
**Option C:** This option is incorrect because the antiseptic property of bleaching powder is not primarily due to its ability to alter the pH of its surroundings.

**Clinical Pearl / High-Yield Fact**
It is essential to note that hypochlorous acid is a highly reactive compound and should be handled with caution. Prolonged exposure to hypochlorous acid can cause skin and eye irritation, as well as respiratory problems.

**Correct Answer:** D.