Is it possible that two types of dislocation coexist. a) - True b) - False

yes it is possible

Explanation:

dislocation are if two type edge and screw dislocations

edge dislocation is a defect where an extra half plane is inside the lattice.

and screw dislocation is one in which can be assumed as the first half of the crystal slips over another.

These dislocation can coexist together where the line direction and burger vectors are neither parallel nor perpendicular then at that condition both dislocation screw and edge will coexist