Answer : 3. "ribosome"
Explanation :

 Protein synthesis takes place in the cell on ribosomes. Ribosomes are cellular structures composed of RNA and proteins, and they are the sites where amino acids are linked together to form proteins, following the instructions encoded in messenger RNA (mRNA) molecules. This process, called translation, is a fundamental cellular mechanism essential for the synthesis of various proteins necessary for the functioning of the cell and the organism as a whole. Ribosomes can be found both in the cytoplasm of the cell and attached to the endoplasmic reticulum in eukaryotic cells.