The junction type that lets neighboring cells exchange small molecules is the

Gap junctions.

Explanation:

Gap junctions may be defined as the intercellular connection present between the cells of the animals. They are made of the connexons and present in all cells of the body except skeletal muscles.

The small molecules and ions can easily pass through the gap junctions. The neighbouring cells can pass the molecules and communicates with each other through the gap junctions. They are known as  macula communicans. Invertebrates have the gap junction made of innexin.

Thus, the answer is gap junctions.

i think its the first one