Which of the following is NOT a product of hydration of cement?

The product that is NOT created by the hydration of cement is Di calcium silicate.
The process of hydration of cement involves several stages and produces the following:

Calcium silicate hydrate (C-S-H gel): Primary binder in concrete
Calcium hydroxide: Byproduct, also referred as 'lime,' contributes to strength but in a lesser degree than C-S-H gel
Calcium aluminate hydrate: These phases contribute to strength development in a shorter time span, particularly during the initial stages of curing.
The di calcium silicate, however, is part of the original Portland cement and not a product of hydration. During the hydration process, it further reacts with water to produce Calcium silicate hydrate and Calcium hydroxide.