Question

What property of carbon allows it to form very large, complex, 3-dimensional molecules?

Answer 1

Its ability to catenate, to form long `C-C` chains.........

Explanation:

And not only can carbon form long chains, along the chain, heteroatoms, oxygen, nitrogen, sulfur, can be substituted, which gives rise to very diverse chemistry, from which, as far as we know, a biology eventually arose.

See this old answer.