Abasalt forms under which of the following conditions?
an intermediate lava cooling at earth's surface.
a mafic lava cooling at earth's surface.
a silicic magma cooling deep underground.
a silicic lava cooling at earth's surface.
a mafic magma cooling deep underground.

A mafic lava cooling at earth's surface

Explanation: Basalt is the mafic igneous rock formed by the cooling of the magnesium rich and iron rich lava exposed area rapidly.It is mostly  crushed for the purpose of using in construction projects. So,when mafic lava cools down on the surface of the Earth it forms basalt or basaltic lava . It is usually found in the form of columns on the Earth's surface.