when looking for Endoplasmic reticulum of a cell, the microscope zooms in enough to see ribosomes that are embedded in the outside of the Endoplasmic Reticulum. Which type of Endoplasmic Reticulum is this

Rough ER

Explanation:

This type of Endoplasmic Reticulum has ribosomes around its outer membranes hence is a major organelle in the processing of cell proteins. When polypeptide chains are formed in the ribosomes, they enter the lumen of the RER where they are folded properly using chaperones and post-translational modification carried out on them.