Which of the following best describes viscosity, and under which conditions does magma exhibit high viscosity?

• A. Viscosity is a measure of a fluid's ability to conduct electricity; magma has high viscosity when it contains many dissolved ions.
• B. Viscosity is a measure of a fluid's color intensity; magma has high viscosity when it is dark in color.
• C. Viscosity is a measure of a fluid's resistance to flow; magma has high viscosity when it contains a high amount of silica and is at a lower temperature.
• D. Viscosity is a measure of a fluid's density; magma has high viscosity when it is at a high temperature and contains little silica.

Answer: (C)

Verified step by step guidance

1. Understand the definition of viscosity: Viscosity is a measure of a fluid's resistance to flow, meaning how thick or sticky the fluid is and how easily it moves.
2. Recognize that viscosity is not related to electrical conductivity, color intensity, or density, but specifically to flow resistance.
3. Identify factors that affect magma viscosity: Magma viscosity increases with higher silica content because silica forms complex networks that make the magma thicker.
4. Note that temperature also affects viscosity: Lower temperatures increase viscosity because cooler magma is less fluid and flows more slowly.
5. Combine these concepts to conclude that magma exhibits high viscosity when it contains a high amount of silica and is at a lower temperature.