Final answer:
A volcano may occur when hot magma is forced up through the Earth's crust from the mantle, which is capable of producing magma due to various melting processes and the presence of mantle plumes from the core-mantle boundary. Therefore, the correct option is 3).
Step-by-step explanation:
When hot magma is forced from the Earth's mantle up through the crust, a volcano may occur. The mantle is the layer within the Earth that lies beneath the crust and above the core. It is capable of deforming and flowing slowly, which includes the process of convection where heat escapes from the interior to the upper mantle. The mantle is where most of the magma originates, due to processes such as decompression melting, flux melting, and the addition of heat. Mantle plumes, which can cause melting of the lithospheric region and create hot spots, are thought to be generated at the core-mantle boundary and can cause volcanoes to form at any point above them, irrespective of plate boundaries.
Therefore, the correct option is 3).