#### Which of the following statements is true regarding physical quantities?Option: 1 Physical quantities can be defined only by their units.Option: 2 Physical quantities can be defined only by their magnitudes.Option: 3 Physical quantities can be defined by both their units and magnitudes.  Option: 4 Physical quantities cannot be defined.

Physical quantities are properties of objects that can be measured quantitatively. These properties can be described in terms of both their magnitude (numerical value) and their unit of measurement. The unit of measurement represents the standard against which the magnitude of the physical quantity is measured.

Option A is incorrect because physical quantities cannot be defined only by their units, as the magnitude of the quantity is also an important part of its definition. For example, the unit of length is metres, but a specific length is defined by its numerical value as well.

Option B is incorrect because physical quantities cannot be defined only by their magnitudes, as the unit of measurement is necessary to specify the magnitude of the quantity. For example, the value "10" could represent a length of 10 metres, a time of 10 seconds, or a mass of 10 kilograms.

Option D is incorrect because physical quantities can be defined, as they are measurable properties of objects.

So, The correct answer is Option 3.