Final answer:
The mantle is the layer of Earth with the largest volume, constituting the bulk of Earth's interior beneath the crust. While the core is substantial in size, the mantle's thickness of roughly 2,900 km makes it far larger by volume. The crust is the thinnest and outermost layer and is not the largest by any measure. Option a. Core is the correct answer.
Step-by-step explanation:
When examining the internal structure of the Earth, we see multiple layers, each with distinct characteristics. The question posed asks which layer has the largest volume among Earth's physical layers. To answer this, we refer to the composition of the Earth that includes the core, mantle, and crust, as well as their respective thicknesses. The core, while significant, is not the largest by volume. The crust is the outermost layer and is relatively thin. The mantle, according to its description, extends approximately 2,900 km beneath the Earth's surface, making it substantially thicker than the crust or the core.
The mantle is described as having an ultramafic composition with more iron, magnesium, and less aluminum and silicon than the crust. Due to its massive thickness and large extent, the mantle constitutes the largest volume of Earth's three chemical layers, surpassing the core which is mostly composed of iron and nickel. Thus, the correct answer to the student's question is the mantle, indicated by choice 'b. Mesosphere,' although the more accurate term for the entire mantle should be used.
It's important to note that the term 'mesosphere' can sometimes be confused with a layer of the atmosphere, but in this context, the mantle is the correct term for the largest volume layer of Earth's layers as it is primarily a geological term. The lithosphere comprises both the crust and the upper part of the mantle, making it different from just the 'mantle' as described in the question.