The Question is from neet-chemistry surface-chemistry colloidal-state, and it was created by the author Mr. S M HUSSAIN

Question

A colloidal solution of gold nanoparticles exhibits a ruby red color. This phenomenon is primarily attributed to:

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**:  Surface Plasmon Resonance (SPR) and light scattering in colloidal solutions.
 **Related Topics**: Colloidal chemistry, nanomaterials, spectroscopy, Tyndall effect.
 **Prerequisites**: Understanding of light-matter interactions, electromagnetic radiation, and the properties of colloidal solutions.
## SOLUTION PATHWAY
**Given Information**:
A colloidal solution of gold nanoparticles appears ruby red.
**Method & Steps**:
1. Analyze the color observed.
  Reasoning: The ruby red color indicates that the solution transmits red light and absorbs other wavelengths.
2. Consider the properties of gold nanoparticles.
  Working: Gold nanoparticles of a specific size exhibit surface plasmon resonance (SPR).  SPR is a phenomenon where the collective oscillation of conduction electrons in the nanoparticles interacts with incident light. This interaction leads to strong absorption and scattering of light at specific wavelengths.
  Key Point: The size and shape of the nanoparticles strongly influence the wavelength of light absorbed and scattered.
3. Identify the dominant interaction.
  Result: For gold nanoparticles of a size resulting in a ruby red color, scattering (Tyndall effect) is a significant factor contributing to the color, though absorption also plays a role.  The Tyndall effect is the scattering of light by particles in a colloid.  Since the particles are larger than the wavelength of visible light, Rayleigh scattering is not the dominant effect. Mie scattering dominates and results in the characteristic color. 
  Verification: The Tyndall effect is a well-established phenomenon observed in colloidal solutions, and the ruby red color of gold nanoparticles is a classic example.
## OPTION ANALYSIS
A :x: Absorption of light in the red region would lead to the solution appearing blue-green (complementary color), not red.
B :x: Fluorescence is a process where a substance absorbs light at one wavelength and emits light at a longer wavelength. While gold nanoparticles can exhibit fluorescence under certain conditions, it's not the primary reason for their ruby red color in a colloidal solution.
C ✓: The Tyndall effect accurately describes the scattering of light by the gold nanoparticles, contributing significantly to the observed ruby red color.
D :x: Refraction of light by the dispersion medium (the liquid) has a minimal effect on the overall color of the solution; the scattering by the nanoparticles is the dominant factor.
## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing absorption and scattering:  Understanding the difference between absorption and scattering of light is crucial for correctly interpreting the color of colloidal solutions.
  2.Overlooking the size dependence of SPR: The wavelength of light absorbed and scattered by nanoparticles strongly depends on their size and shape.
 **Quick Tips**:
  1.Remember that colloidal solutions scatter light, leading to the Tyndall effect.
  2.The color observed is often related to the wavelength of light that is *not* absorbed (transmitted and scattered).

Mr. S M HUSSAIN · Answer

Absorption of light in the red region of the spectrum by gold nanoparticles

Mr. S M HUSSAIN · Answer

Fluorescence of gold nanoparticles upon excitation with white light

Mr. S M HUSSAIN · Answer

The correct Option is "Scattering of light by the gold nanoparticles (Tyndall effect)"

Mr. S M HUSSAIN · Answer

Refraction of light by the dispersion medium

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