The correct option is (c).
Explanation
Sweating, or perspiration, is a physiological mechanism primarily associated with thermoregulation and excretion in mammals.
Statement 1 is Correct. Sweat is a fluid secreted by sweat glands in the skin. It is composed primarily of water (about 99%) and dissolved salts (electrolytes), mainly sodium chloride. It may also contain trace amounts of urea, lactic acid, and other metabolic waste products.
Statement 2 is Incorrect. The primary function of sweating is to lower body temperature, not increase it. This process works through evaporative cooling. As sweat evaporates from the surface of the skin, it absorbs latent heat from the body, thereby cooling it down and maintaining homeostasis during physical exertion or high environmental temperatures.
Statement 3 is Correct. During the summer or periods of intense physical activity, sweat is produced in larger quantities. When the water content of the sweat evaporates, the dissolved salts (specifically sodium chloride) are left behind. These salts crystallize and form visible white patches on clothes, particularly in the underarm and back areas.
Key Takeaway: Sweating is a thermoregulatory process that cools the body through evaporation; the fluid consists mainly of water and salts, which leave residue upon drying.