To solve this problem, we need to analyze each statement regarding factors affecting the rate of photosynthesis:$\newline \bullet$Option 1: Increasing atmospheric CO2 concentration up to 0.5% can enhance CO2 fixation rate.$\newline$ - This statement is correct. Increasing CO2 concentration can enhance the rate of photosynthesis up to a certain point, as CO2 is a substrate for the Calvin cycle.$\newline \bullet$Option 2: C3 plants respond to higher temperatures with enhanced photosynthesis while C4 plants have much lower temperature optimum.$\newline$ - This statement is incorrect. C3 plants generally have a lower temperature optimum compared to C4 plants. C4 plants are adapted to higher temperatures and have a higher temperature optimum for photosynthesis.$\newline \bullet$Option 3: Tomato is a greenhouse crop which can be grown in CO2 – enriched atmosphere for higher yield.$\newline$ - This statement is correct. Tomatoes can benefit from CO2 enrichment in greenhouses, leading to increased photosynthetic rates and higher yields.$\newline \bullet$Option 4: Light saturation for CO2 fixation occurs at 10% of full sunlight.$\newline$ - This statement is correct. Light saturation for photosynthesis can occur at relatively low light intensities, often around 10% of full sunlight, depending on the plant species.$\newline$Therefore, the statement that is not correct is Option 2.$\newline$The correct answer is Option 2.