Ozonolysis of an organic compound gives formaldehyde as one of the products. This confirms the presence of 

a vinyl group

The correct answer is option 1. a vinyl group.

If ozonolysis of an organic compound yields formaldehyde as one of the products, it indeed provides valuable information about the structure of the original compound.

Ozonolysis of a vinyl group:

Therefore, if formaldehyde is one of the products of ozonolysis, it suggests the presence of a vinyl group in the original compound, where the ozonolysis directly yields formaldehyde. So, the correct answer is: A vinyl group.