Answer :
They will be basalt. Formed by volcanic activity on the seafloor, thus the water will contribute that the magma is cooled very quickly and make it fine grained. This usually happens where the seafloor is spreading, on the line that separates two tectonic plates. These rocks are extrusive rocks.
Fine-grained igneous rocks that have small grains cooled rapidly and are likely to be basalt extrusive rocks.
Explanation:
Extrusive igneous rocks are the type of igneous rocks (crystallize from a liquid) which are created when magma reaches the surface of Earth a volcano and cools rapidly. Basalt, one of the examples or the types of an extrusive igneous rock that is the most common type and the most common rock type at the Earth's surface. Basalt is a fine-grained rock which is mainly composed of pyroxene and plagioclase. Extrusive igneous rocks are formed when the molten rock flows above the surface as lava and then cools down. This lava comes between 50 km and 150 km below the surface of Earth from the upper mantle layer.