Symmetry in Glycerol Positions Limits Distinct Triglycerides

Steps:

• Glycerol has three hydroxyl groups: two equivalent primary (sn-1, sn-3) and one secondary (sn-2).
• With three different fatty acids (L, O, P), assign one to sn-2: 3 choices.
• Assign remaining two to sn-1 and sn-3: swapping them yields identical molecules due to symmetry.
• Total distinct arrangements: 3 (one for each choice in sn-2).

Why A is correct:

• The formula for stereospecific numbering (sn) in glycerol defines sn-1 and sn-3 as indistinguishable, reducing permutations from 6 to 3.

Why the others are wrong:

• B: Ignores symmetry, undercounts by treating all positions as distinct but not fully (would be 6 if no symmetry).
• C: No basis; possibly confuses with partial distinctions.
• D: Assumes all 3! = 6 permutations plus extras, overlooking glycerol's mirror plane.

Final answer: A