To solve this problem, we need to identify the mismatch between the given pairs. Let's analyze each option:$\newline \bullet$Option 1: Rhodospirillum – Mycorrhiza$\newline$ - Rhodospirillum is a genus of purple non-sulfur bacteria, which are photosynthetic and do not form mycorrhizal associations.$\newline$ - Mycorrhiza refers to a symbiotic association between fungi and plant roots.$\newline$ - Therefore, this is a mismatch.$\newline \bullet$Option 2: Anabaena – Nitrogen fixer$\newline$ - Anabaena is a genus of cyanobacteria known for its ability to fix atmospheric nitrogen.$\newline$ - This is a correct match.$\newline \bullet$Option 3: Rhizobium – Alfalfa$\newline$ - Rhizobium is a genus of bacteria that forms symbiotic relationships with legumes, such as alfalfa, to fix nitrogen.$\newline$ - This is a correct match.$\newline \bullet$Option 4: Frankia – Alnus$\newline$ - Frankia is a genus of actinobacteria that forms symbiotic nitrogen-fixing associations with plants like Alnus (alder).$\newline$ - This is a correct match.$\newline$Based on the analysis, the mismatch is in Option 1: Rhodospirillum – Mycorrhiza.$\newline$Therefore, the correct option is Option 1.