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: Algin and carrageen are products of algae.$\newline$ - Algin is derived from brown algae, and carrageen is obtained from red algae.$\newline$ - This statement is correct.$\newline$• Option 2: Agar-agar is obtained from Gelidium and Gracilaria.$\newline$ - Agar-agar is indeed extracted from these red algae.$\newline$ - This statement is correct.$\newline$• Option 3: Chlorella and Spirulina are used as space food.$\newline$ - Both Chlorella and Spirulina are rich in proteins and nutrients, making them suitable for space food.$\newline$ - This statement is correct.$\newline$• Option 4: Mannitol is stored food in Rhodophyceae.$\newline$ - Mannitol is actually a storage product in Phaeophyceae (brown algae), not Rhodophyceae (red algae).$\newline$ - This statement is incorrect.$\newline$Therefore, the wrong statement is Option 4.