Question

Given below are two statements: one is labelled as Assertion A and other is labelled as Reason R.
Assertion A : Finest gold is red in colour, as the size of the particles increases, it appears purple then blue and finally gold.
Reason R : The colour of the colloidal solution depends on the wavelength of light scattered by the dispersed particles.
In the light of the above statements, choose the most appropriate answer from the options given below.

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Answer 1

The Correct Option is A

The given question involves assessing the truthfulness of an assertion and a reason, followed by determining the logical relationship between them. Let's break down both statements to understand them better:

1. Assertion A: "Finest gold is red in colour, as the size of the particles increases, it appears purple then blue and finally gold."
   • This statement relates to the optical properties of colloidal suspensions of gold. When gold particles are extremely small, they exhibit a phenomenon known as surface plasmon resonance, which results in different colors based on the size of the particles.
   • Smaller particles can appear red, while larger particles progressively show colors like purple, blue, and gold as their size increases. This is a result of the particles scattering light of different wavelengths; hence, this assertion is true.
2. Reason R: "The colour of the colloidal solution depends on the wavelength of light scattered by the dispersed particles."
   • This explanation aligns with the science of light scattering. The phenomenon is largely due to the particle size relative to the wavelength of visible light.
   • As particles scatter different wavelengths of light, the scattered light determines the color perceived. Hence, this statement is also true.

To determine if the reason provided is the correct explanation of the assertion, we need to see if the change in color with particle size can be attributed to the scattering of light at different wavelengths:

• Since the assertion describes a sequence of color changes as particle size increases, and because the reason directly explains this phenomenon based on changes in light scattering, the reason accurately justifies why we observe this color transition in colloidal gold solutions.

Given this analysis, the most appropriate answer is: Both A and R are true and R is the correct explanation of A.