In which of the following group of organisms, syngamy occurs outside the body of the organism ?

Syngamy or fertilization refers to fusion of gametes.

Syngamy is external (outside the body of an organism or in the water) in most of the green algae and some brown algae.

(1) In mosses, fertilization or syngamy takes place inside an archegonium.

(3) In ferns, fetilisation or syngamy takes place inside the archegonium. 

(4) In most fungi, fertilization takes place inside the body.