Which are the most common producers in aquatic ecosystems?
a - bacteria
b -algae
c -fish
d -plants

b -algae

Explanation:

The most common producers in aquatic ecosystems are the algae. They are called phytoplanktons.

In the food web and food chain of aquatic ecosystems, they usually set out with the algae. These algae are called phytoplanktons. They are the producers in all aquatic ecosystem. Phytoplanktons consists of algae and cyanobacteria. Just like plants on land, phytoplanktons manufacture food in an aquatic ecosystem.

6.817 x 10^-4

Explanation:

First move the decimal between the ones and tenths (6.8), then count back to the original decimal point if you are counting to the left then its going to be a negative exponent but if you count towards the right it'll be a positive exponent. From 6.817 to 0.0006817, it is 4 places back, nd this is how you get the answer.