Alginic Acid's Block Copolymer Structure

Steps:

• Identify alginic acid as a linear polysaccharide from brown seaweed cell walls, composed of mannuronic and guluronic acid units.
• Note the diagram likely shows alternating or block arrangements of these two uronic acid monosaccharides.
• Recognize that the polymer features regions where the two sugars link in sequences with differing stereochemistry, resembling opposed orientations.
• Compare to options, eliminating those mismatched to known 1→4 β-glycosidic bonds and linear form.

Why B is correct:

• Alginic acid consists of β-D-mannuronic and α-L-guluronic acids in block or alternating sequences, creating opposite directional arrangements along the chain, unlike uniform glycogen.

Why the others are wrong:

• A: Bonds are 1→4, not 1→6; it's not solely hexose-based without uronic modifications.
• C: Involves only uronic acid monomers via glycosidic bonds, not hexoses and water directly.
• D: While 1→4 bonds are present, it requires two specific uronic monomers, not generic ones.

Final answer: B