Which of the following is not a vector quantity?

Vector quantities are defined as quantities having magnitude as well as direction. For example, velocity is a vector quantity as it gives the speed of an object with direction. Similarly, acceleration is a vector quantity as it gives the magnitude of acceleration with the direction. Force of an object is equal to mass*acceleration, therefore acceleration is also a vector quantity. However, mass is not a vector quantity but a scalar quantity since it gives only the magnitude. Hence, option D is correct.