What conditions make for a violent volcanic eruption?
a. magma that can flow easily
b. magma with low gas content
c. magma with low silica content
d. magma with high viscosity

The correct answer is (d) Magma with high viscosity.

The magma with high viscosity has chances of violent volcanic eruption. The magma creates pressure inside the volcano by increasing the viscosity of magma. The magma having high viscosity has has high gas content which seems like a soft drink infused with gas bubbles which will erupt when sufficient pressure is created inside it. This results in eruption of volcano in a violent way.