To solve this problem, we need to evaluate each statement to determine which one is incorrect.$\newline$Let's analyze each option:$\newline$• Option 1: Cyanobacteria are also called blue-green algae.$\newline$ - This statement is correct. Cyanobacteria are commonly referred to as blue-green algae due to their color and photosynthetic capabilities.$\newline$• Option 2: Golden algae are also called desmids.$\newline$ - This statement is incorrect. Golden algae belong to the class Chrysophyceae, while desmids are a group of green algae belonging to the class Charophyceae.$\newline$• Option 3: Eubacteria are also called false bacteria.$\newline$ - This statement is incorrect. Eubacteria are true bacteria, not false bacteria. The term "false bacteria" is not used for eubacteria.$\newline$• Option 4: Phycomycetes are also called algal fungi.$\newline$ - This statement is correct. Phycomycetes, also known as lower fungi, are sometimes referred to as algal fungi due to their simple structure and resemblance to algae.$\newline$Analyzing the options, we find that Option 3 is the incorrect statement.$\newline$Therefore, the correct answer is Option 3.