a solution
Nail and sand would be considered a heterogeneous mixture because the two substances do not mix uniformly and can be easily separated.
homogeneous mixture
That would be a homogenous mixture.
A mixture with two or more substances spread evenly throughout is called a homogeneous mixture. This means that the different substances are uniformly distributed at a molecular level, resulting in a consistent composition throughout the mixture.
Solution
It is called a heterogeneous mixture.See the Related Questions for more information.
When two things don't mix, it is called immiscibility. This can happen when substances do not dissolve or blend together to form a homogeneous mixture.
homogenous mixture
suspension
A heterogeneous mixture is a mixture of two or more substances that are not uniformly distributed. The iodine and water in the question are not homogeneous because they are not uniformly distributed.
Suspensions and colloids are two types of particles that do not mix uniformly when put together. Suspensions contain larger particles that settle over time, while colloids have smaller particles that remain dispersed throughout the mixture.
You get a mixture.