The question asks for the number of optically active compounds from the following, but the actual list/structures of compounds is missing from the prompt.

Without the given compounds, it is impossible to determine how many are optically active.

What is needed

To solve this, I need the structures or names of the compounds referred to by “the following”. Then I can check for:

1. Chiral centers
2. Plane/center of symmetry
3. Meso forms
4. Restricted rotation / axial chirality, if relevant

and count how many are optically active.

About the stored answer

The stored correct answer is given as 1, but since the compounds themselves are not visible, I cannot independently verify it from the provided information.

Therefore, I cannot honestly derive the answer from the current prompt alone.