What is a characteristic of a weak alkali?

A characteristic of a weak alkali is that it softens the stratum corneum of the skin. Weak alkalis, typically having a pH above 7 but not very high, can interact with the proteins and lipids in the outermost layer of the skin. This interaction can lead to a mild, keratolytic effect, which means they can help to loosen and slough off dead skin cells, making the skin feel softer and smoother.

Understanding the chemistry of weak alkalis helps clarify their role in various skincare products. They are often used in formulations designed to exfoliate or to enhance penetration of active ingredients into the skin. The ability to soften the stratum corneum without causing significant irritation or damage distinguishes weak alkalis from stronger, harsher bases that can cause more severe effects on the skin.

In contrast, stronger alkalis are more likely to corrode skin tissue or increase skin acidity, which is not typical behavior for weak alkalis. Additionally, weak alkalis would not have a pH below 5, as a pH below 7 indicates an acidic nature. Thus, option C accurately reflects the properties of a weak alkali.