Choose the correct statement

detailed solution

Correct option is D

Temperature is a scalar as temperature has magnitude only. But temperature gradient (rate of change of temperature) is positive if temperature increases in a specified direction and negative in the opposite direction. So temperature gradient is a vector. A body can move in a specified direction, so its velocity is vector quantity, but light is energy, it can propagate in all possible direction in the from of electro-magnetic wave. So velocity of light has no specified direction, it is scalar. Electric current density at a point is a vector quantity, its direction is same as the direction of flow of positive charge through that point. So option (4) is correct.