A vector is a mathematical quantity that has both magnitude and direction. It is represented by an arrow, with the length of the arrow representing the magnitude and the direction of the arrow representing the direction.
A scalar is a mathematical quantity that only has magnitude, and no direction. Examples of scalars include mass, temperature, and time.
If the quantity has both magnitude and direction, it is a vector. If it only has magnitude, it is a scalar. Another way to determine this is by looking at the units – vectors will have both a magnitude and direction unit, while scalars will only have a magnitude unit.
No, a quantity is either a vector or a scalar, it cannot be both. However, some quantities can be represented as both a vector and a scalar, depending on the context. For example, velocity can be represented as both a vector (with direction) and a scalar (speed, without direction).
A quantity is "not applicable" in terms of vector or scalar if it does not have a clear magnitude or direction. This can happen when the quantity is undefined, or when it does not have a physical meaning in terms of magnitude and direction. For example, a person's name or a color cannot be represented as a vector or scalar.