Which one is the vector quantity?
A) Time
B) Temperature
C) Flux density
D) Magnetic field intensity

Hint: We know that all measurable quantities are called physical quantities. most of the physical quantities are classified into scalars and vectors. A scalar quantity has only magnitude whereas a vector quantity has both magnitude and direction.

Complete step by step answer:
Here, time and temperature both are scalar quantities, which have only magnitude no direction. To see time like 5hr, 4min, or 7-second the only magnitude is enough no need of direction to represent time.
And also temperature can be written $263K$, $27^{\circ}C$, or $320F$ the only magnitude is enough to specify temperature and direction is not necessary.
Magnitude is enough to represent a given quantity with no need for direction.
Magnetic field intensity is the strength of the magnetic field. That is a space or region equal to the force experienced by a unit charge moving with unit velocity perpendicular to the direction of the magnetic field at that point. Here direction is very important to specify force acting. Hence magnetic field intensity is a vector quantity, which has both magnitudes as well as direction.
Here time and temperature are the fundamental quantity that cannot be derived from any quantity, which is independent of other quantities. But magnetic flux density and magnetic field intensity both are derived quantities.
Flux density is also a scalar quantity, which is a large number of magnetic field lines crossing per unit volume area, the largest is flux density.
The Vector is represented by an arrow mark on the symbol. For example, force is a vector quantity that is represented by $\overrightarrow F $. Here, the arrow mark represents the direction, and magnitude is represented by f (without arrow mark).
From all these observations we can say that Magnetic field intensity is a vector quantity.

$\therefore $Magnetic field intensity is a vector quantity. Hence, the correct option is (D)

Note:
(i) To describe a scalar quantity, we require (a) the specific unit of that quantity and (b) the number of times that unit is contained in that quantity.
(ii) To describe a vector quantity, we require is (a) the specific unit of that quantity (b) the number of times that unit is contained in that quantity, and (c) the orientation of that quantity.