A population of 100 butterflies living on an acre of land loses three-quarters of its members when a sudden freeze in the spring occurs just after they emerge as caterpillars. This population has undergone a reduction in population size due to

The correct answer is - a density independent factor.

Explanation:

Any external cause or change that leads to the change in the size of a population regardless of the density of the particular population known as a density independent factor in ecology.

Density independent factors are the factors that are not affected by the size of the population size of the species such as weather, climate and natural disasters.

Thus, the correct answer is -  a density independent factor.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.