What process allows the drops to spread out in the fish tank?

diffusion

Explanation:

The process that allows the drops to spread out in the fish tank is called diffusion.

Diffusion is defined the movement of a substance from a region of high concentration to that of low of concentration.

The drop will spread out in the fish tank by diffusion because it is more concentrated than the water surrounding it in the tank.

Perfumes are able to spread out in a room by this process. A rotten smell dissipates across the environment through this mechanism also.

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.