Which of the following are not primary producers in an aquatic ecosystem?

Match the List-$I$ with List-$II$:

List-$I$	List-$II$
$a$. Carbon dissolved in oceans	$i$. $55$ billion tons
$b$. Annual fixation of carbon through photosynthesis	$ii$. $71 \%$
$c$. $PAR$ captured by plants	$iii$. $4 \times 10^{13} \ kg$
$d$. Productivity of oceans	$iv$. $2$ to $10 \%$

Choose the correct answer from the options given below:

Consider the following statements about food chain:
$I.$ The transfer of energy from producers to top consumers through a series of organisms is called a food chain.
$II.$ $A$ food chain is always straight and proceeds in a progressive straight line.
$III.$ In a food chain,there is a unidirectional flow of energy from the sun to producers and subsequently to a series of different types of consumers.
Which of the statements given above are correct?

Which of the following is $NOT$ a functional unit of an ecosystem?

Which of the following processes occurs at a faster rate?

Which of the following has the largest population in a food chain?