Definite articles are used for something already mentioned.
Did you see Frozen 2? I liked the movie.
Is a definite article necessary in the following case?
I form five groups. The leaders of the groups are active.
As the first sentence mentions "five groups," the may be necessary.
Question 1: Is The necessary even though I mention "leaders" for the first time?
Question 2: Is The necessary because followed by "of the groups?"