What is formed when starch is completely hydrolysed?

Step 1: Analyze the question The question asks for the final product when starch is completely hydrolysed. The word "completely" is the key.

Step 2: The concept Starch is a polysaccharide, a long chain of glucose units joined by glycosidic bonds. Hydrolysis means breaking these bonds using water, with an acid or an enzyme as the catalyst.

Hydrolysis happens in stages:

• Starch → (partial hydrolysis, e.g. by amylase) → maltose (a disaccharide, 2 glucose units)
• Maltose → (further hydrolysis, e.g. by maltase or dilute acid) → glucose (a monosaccharide)

Step 3: Overall equation

(C₆H₁₀O₅)ₙ + nH₂O → nC₆H₁₂O₆

Starch + water → glucose (with dilute acid and heat, or enzymes)

Step 4: Check the other options

• Fructose: a monosaccharide, but it is not a product of starch hydrolysis. It comes from sucrose along with glucose.
• Lactose: milk sugar, which hydrolyses to glucose and galactose.
• Maltose: an intermediate product of partial hydrolysis only.
• Sucrose: table sugar, which hydrolyses to glucose and fructose.

Answer: B. glucose

Exam tip: Remember the word "completely." Partial hydrolysis of starch gives maltose, while complete hydrolysis gives glucose. Starch → Maltose → Glucose.