Which of the following groups of substances are not six-carbon compounds?

Analyze the question: We need the group of substances that are not six-carbon compounds. Let's check the carbon count of each substance.

Concept: carbon content of each substance

• Glucose (C₆H₁₂O₆): a six-carbon monosaccharide (hexose).
• Lactose (C₁₂H₂₂O₁₁): a disaccharide of glucose + galactose. It has 12 carbons in total, though it is built from two six-carbon units.
• Cellulose (C₆H₁₀O₅)ₙ: a polysaccharide, a long chain of glucose units. It is a polymer, not a single six-carbon compound, though its repeating unit has six carbons.
• Pyruvate (C₃H₄O₃): a three-carbon compound, the end product of glycolysis.

Step-by-step evaluation of the options

• A. Glucose and lactose: glucose has 6 C, but lactose has 12 C. This is a mixed group.
• B. Lactose and cellulose: lactose has 12 C, and cellulose is a polymer of many hexose units. Neither is a simple six-carbon compound, so this fits "not six-carbon compounds" fairly well.
• C. Glucose, lactose and pyruvate: glucose is a six-carbon compound, so the group does not qualify.
• D. Pyruvate and cellulose: pyruvate has 3 C, and cellulose is a large polymer, so neither is a six-carbon compound.

Which is best, B or D? Both B and D contain substances that are not strictly six-carbon molecules. However, the question asks for a group that are not six-carbon compounds, and pyruvate is the clear, definite non-six-carbon substance (3 C). Lactose and cellulose are both built from six-carbon sugar units (hexoses), so in a typical WASSCE treatment they are loosely classed as "six-carbon sugar" compounds.

Answer: D. Pyruvate and cellulose

Exam tip: Remember the carbon counts: pyruvate = 3 C, glucose, fructose and galactose = 6 C, and disaccharides and polysaccharides are made of six-carbon units. When two options both look right, choose the one containing the most clear-cut example, here pyruvate, the famous 3-carbon product of glycolysis.