Question

Calculate the relative density of zinc when its density is \[7{{ }}gc{m^{ - 3}}\].
(A) 0.7
(B) 3.5
(C) 49
(D) 7

Answer 1

Hint: The given problem is from basic properties of material. The magnitude of density of any substance is equal to the magnitude of its relative density. We use this statement to find out the solution to a given problem.

Complete step by step answer:
As we know that the relative density is defined as the ratio of density of any substance to the density of water at . The density of water at temperature is \[1{{ }}gc{m^{ - 3}}\].
Thus the magnitude of density of any substance is equal to the magnitude of its relative density. The relative density is the ratio of two similar quantities, so it has no unit.

According to the given question, zinc has its density as \[7{{ }}gc{m^{ - 3}}\]. So the value of relative density of zinc is defined as the ratio of density of substance to the density of water at .
As we know that the density of water at temperature is 1 g/$cm^3$. So the relative density of zinc will be equal to the magnitude of its relative density. That will be equal to \[7{{ }}gc{m^{ - 3}}\].

Hence, the correct answer is option (D).

Density is the amount of mass in a unit volume of matter, every substance has a different density. The water is taken as a reference substance to calculate the relative density of other substances with respect to water.

Note: Sometimes we take the density of water in \[kg{m^{ - 3}}\] which gives the wrong result. We should always check the unit of a given substance and then put the same unit for the reference substance in the formula to calculate the right result.