Final answer:
Eumelanin is the type of melanin responsible for giving hair black and brown colors. It is produced by melanocytes and defines hair color, which can change with age as melanin production decreases. Hence option A is correct.
Step-by-step explanation:
The type of melanin that lends black and brown colors to hair is known as eumelanin. Hence option A is correct. This pigment is produced by melanocytes within the hair papilla and is the primary determinant of hair color. The presence of more eumelanin gives hair a darker color, and its lower levels result in lighter hair colors. Over time, melanin production can decrease, leading to gray or white hair.
Pheomelanin (Option b): This type of melanin produces red and yellow pigments and is responsible for the color variations in red hair and freckles.
Trichosiderin (Option c): Trichosiderin is not melanin; it is a pigment that may be present in red or rust-colored hair but is less common.
Neuromelanin (Option d): Neuromelanin is a type of melanin found in the brain, specifically in neurons. It is not involved in the coloration of hair.
In summary, eumelanin, specifically black and brown eumelanin, is the primary contributor to the dark colors seen in human hair.