Agar-agar is obtained from algae belonging to the class
The correct option is B Rhodophyceae
Agar-agar is obtained from members of red algae or rhodophyceae such as Gracilaria and Gelidium.
Phaeophyceae or brown algae include the giant marine algae such as kelps.
Chlorophyceae are green algae and include single cellular forms such as Chlorella and Chlamydomonas and also multicellular colonial forms such as Volvox.
Bacillariophyceae are protists and include diatoms.