The fine grained texture of most of the igneous rock formed on the surface of iceland is due to

Out of the following given choices;

A rapid cooling of the molten rock

B high density of the molten rock

C numerous faults in the island’s bedrock

D high pressure under the island

The answer is; A

When the magma rises from the mantle onto the earth surface in the region, it encounters ice-cold temperatures that cool the magma rapidly. This reduces the time that large mineral crystals (typical of slow-cooling) can form in the cooling rock hence the typical characteristic of these rocks are fine-grained and brittle.  

i think it because equal matrices have equal dimensions, only square matrices can be symmetric. for all indices and . every square diagonal matrix is symmetric, since all off-diagonal elements are zero. in linear algebra, a real symmetric matrix represents a self-adjoint operator over a real inner product space.