New sea floor is created when plates move away from each other what is this type of boundary called ?

A divergent boundary.

Explanation:

When two tectonic plates move away from one another, the space between them must be filled by another substance. Molten rock from the mantle rises up and cools to form new crust.

The information about the creation of "new sea floor" could be considered irrelevant — you only need to focus on what type of tectonic boundary involves two plates moving away from each other. Out of the options of convergent, divergent, or transform boundaries, divergent boundary is the clear answer.