Convex envelope (hull)

Question

I have a question that I can't understand (maybe poorly done)

1) Find the convex envelope of the set $C = \left\{1, 2\right\}$.

Only that. Can you understand?

Answer 1

Assuming that $C$ is seen as a subset of $\mathbb R$, then the answer is $[1,2]$: it is the smallest convex subset of $\mathbb R$ containing $C$.