Which component is referred to as the liquid part of blood?

Plasma is referred to as the liquid part of blood because it constitutes about 55% of total blood volume and is primarily composed of water, salts, and proteins. It serves as a medium for transporting nutrients, hormones, and waste products throughout the body. Plasma plays a crucial role in maintaining blood pressure and regulating body temperature. It contains vital proteins such as albumin, globulins, and fibrinogen, which are essential for various physiological functions, including clotting and immune responses.

The other options do not pertain to the liquid component of blood. Sclerotherapy is a medical treatment aimed at eliminating varicose veins and spider veins, while melasma is a skin condition characterized by dark patches, often due to sun exposure or hormonal changes. Salicylic acid is a topical treatment commonly used for acne and other skin conditions, but it is not related to blood components. Therefore, plasma is distinctly identified as the liquid part of blood.