What determines whether a ribosome will be free or bound?

The ribosome binding signal sequence of the RNA to initiate translation determines whether a ribosome will be free or bound.

Explanation:

Ribosomes help in protein synthesis by participating in translation and linking the amino acids as per the required sequence on the polypeptide chains.  

Free ribosomes are those which synthesize intercellular proteins and bound ribosomes synthesize intracellular proteins.

Ribosomes bind at the ribosome-binding sites located at the mRNA (5’untranslated region) and initiate, regulate, and control the efficiency and accuracy of the translation. This binding site represents upstream of nucleotides with the start codon of mRNA transcript.  

There are four binding points on the ribosomes and one binds to the mRNA and the remaining three binds to the tRNA.  

the answer will be a) proteins i believe