Oxygen binding at the coordination site causes:

a$.$

the iron atom to move from outside the plane of the porphyrin into the plane.

b$.$

the iron atom to move from the plane of the porphyrin outside.

c$.$

movement of the $1$$1$ dimer by approximately $30$ degrees.

d$.$

movement of the $1$$1$ dimer by approximately $115$ degrees.

e$.$

the iron atom to rearrange the electrons to become effectively larger.