Which of the following biologically important coordination compounds has a magnesium central atom? 

Chlorophyll

The correct answer is option 1. Chlorophyll.

Chlorophyll, the green pigment responsible for photosynthesis in plants and algae, contains a magnesium central atom. The magnesium ion is coordinated to the chlorin ring in the structure of chlorophyll. This coordination compound is crucial for capturing light energy during photosynthesis and converting it into chemical energy.