Which type of sexual reproduction is found in $Spirogyra$?

Which of the following organisms cannot fix nitrogen?
$A.$ Azotobacter
$B.$ Oscillatoria
$C.$ Anabaena
$D.$ Volvox
$E.$ Nostoc
Choose the correct answer from the options given below:

In which form is the stored food present in algae?

Which of the following pigments is present in all algae?

Consider the following statements regarding reproduction in class-$Chlorophyceae$.
$I.$ Asexual reproduction is mainly by flagellated zoospores produced in zoosporangia.
$II.$ The sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous,anisogamous and oogamous.
Which of the statements given above are correct?

Select the correct option for the cell wall of green algae.