To solve this problem, we need to analyze each statement about the Endoplasmic Reticulum (ER):$\newline \bullet$Option 1: RER has ribosomes attached to ER$\newline$ - The Rough Endoplasmic Reticulum (RER) is characterized by the presence of ribosomes on its surface, which gives it a "rough" appearance.$\newline$ - This statement is correct.$\newline \bullet$Option 2: SER is devoid of ribosomes$\newline$ - The Smooth Endoplasmic Reticulum (SER) lacks ribosomes, which is why it appears "smooth."$\newline$ - This statement is correct.$\newline \bullet$Option 3: In prokaryotes only RER are present$\newline$ - Prokaryotes, such as bacteria, do not have membrane-bound organelles like the endoplasmic reticulum.$\newline$ - Therefore, neither RER nor SER is present in prokaryotes.$\newline$ - This statement is incorrect.$\newline \bullet$Option 4: SER are the sites for lipid synthesis$\newline$ - The Smooth Endoplasmic Reticulum is involved in the synthesis of lipids, including phospholipids and steroids.$\newline$ - This statement is correct.$\newline$Based on the analysis, the incorrect statement is Option 3.