Question

Assertion: If optical density of a substance is more than that of water then the mass density of a substance can be less than water.
Reason: Optical density and mass density are not related.
A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Assertion is correct but Reason is incorrect.
D) Both Assertion and Reason are incorrect.

Answer 1

Hint: Optical density is a spectroscopic term. It is defined as the ratio of the intensity of light falling upon a material and the intensity of light transmitted. It is the measure of absorbance of a material. Mass density is the mass per unit volume for a substance. We usually refer to mass density as simply density.

Complete step by step solution:
Since optical density is the ratio of the speed of light in two media, the mass density of an optically denser medium can't be less than that of an optically rarer medium.
If we consider the example of turpentine and water, the mass density of turpentine is less than that of water but its optical density is higher. This shows that the mass density of a substance can be less than water if the optical density of a substance is more than that of water. Hence our Assertion statement is correct.
From the descriptions of both mass density, it is clear that these two terms are not related. Hence, our Reason statement is correct.

Hence option (A) is the correct option.

Additional Information:
The mass density of an object can be measured by using Densometer, Pycnometer, Hydrometer, Triple Beam Balance, Graduated Cylinder, etc. Optical density measures how clear or blur a solution is in comparison to water. Optical density is measured using a Photometer or Densitometer. The value of optical density can vary between zero to infinity.

Note: Mass density has obvious importance when it comes to the buoyancy of objects. Mass density can also help to predict the chances of corrosion of substances. Optical density is used in spectrophotometry for estimating the concentration of bacteria or other cells in a liquid.