Which of the following describes molten rock found at depth?

Magma is the term specifically used to describe molten rock that is found beneath the Earth's surface. When rock melts due to extreme heat and pressure, it creates magma, which can accumulate in magma chambers deep within the Earth. This molten rock is enriched with various minerals, gases, and other compounds that can influence its properties and behavior.

Once magma makes its way to the surface through volcanic activity and erupts, it is referred to as lava. Therefore, while both magma and lava are forms of molten rock, the key distinction is that magma is located at depth, whereas lava is the surface manifestation of that magma after an eruption.

Minerals, on the other hand, are solid, naturally occurring substances with a definitive chemical composition, which is fundamentally different from the molten state of magma. The term "electron" does not pertain to geology or rock formations and is instead a subatomic particle relevant to chemistry and physics. Thus, the definition and context of magma as molten rock underground make it the correct choice in this scenario.