Concept:A number system with base 16 is called the hexadecimal system.Explanation:In base 16, each digit position represents a power of 16.It uses digits 0 to 9 and letters A to F for values 10 to 15.The word "hexadecimal" combines "hexa" (six) and "decimal" (ten), meaning 6+10=16.Thus, base 16 is known as hexadecimal.Answer:A. hexadecimal