Nanoparticles are small collections of atoms that can have properties and behaviors that are very different from a bulk sample of the material. Gold and silver are two metals that are able to form nanoparticles with useful properties. One difficulty in the manufactured formation of these particles is avoiding methods that involve toxic chemicals. One potential method for producing gold nanoparticles is to use light energy to reduce gold ions, A u 3 + , to neutral gold metal, A u . The difficulty with this method lies in finding a system that can efficiently capture light energy and convert it into chemical energy. Researchers tested the ability of chloroplasts extracted from two different plant species, one an aquatic pond weed and the other spinach, to use light to create gold nanoparticles.

Question

In a second study, the researchers took spinach extract and varied the concentration of the gold ions in the solution. The solutions were then either exposed to light or kept in the dark for 30 minutes at 24 ∘ C . The data is presented in Figure 2.

In a third study, the researchers used spinach extract with 2 mM gold ions and exposed the solutions to varying intensities of light for varying time intervals at 24 ∘ C . The data is presented in Figure 3.

Which of the following is the BEST explanation for the experimental setup in Study 2?

A Keeping a sample in the dark provides the researchers with a baseline on the rate of nanoparticle formation.
B Keeping a sample in the dark allows the researchers to determine the importance of the gold ion concentration.
C Exposing a sample to a constant light source allows the researchers to determine the rate of gold nanoparticle formation.
D
Exposing a sample to a constant light source allows the researchers to determine how the intensity of the light affects the rate of nanoparticle
formation.

Answer 1

The BEST explanation for the experimental setup in Study 2 is:

A Keeping a sample in the dark provides the researchers with a baseline on the rate of nanoparticle formation.

In this study, by keeping one set of samples in the dark, the researchers can establish a control that helps them understand how much nanoparticle formation occurs without the influence of light. This allows them to compare the results of the light-exposed samples to those kept in the dark, providing a clear baseline for measuring the effect of light on the nanoparticle formation process.