What benefit do small spaces provide in the formation of organic molecules?

The benefit that small spaces provide in the formation of organic molecules is that it creates an additional surface area on which reactions can take place. A larger surface area allows biochemical reactions to take place more frequently, thus increasing the rate of the biochemical reaction. 

substitution is the answer in this case

examples of nucleic acids are deoxyribonucleic acid (dna) and ribonucleic acid (rna).