The bones of the legs of a six years old boy are observed to be weak and crooked. Which of the following…

Step 1: Analyze the question The boy has weak, crooked leg bones. This condition is rickets (bowed legs). We need the elements missing from the mother's diet during pregnancy that affect bone formation.

Step 2: The concept Bones and teeth are made mainly of calcium phosphate. These two minerals give bones their hardness and strength.

• Calcium hardens bones and teeth.
• Phosphorus combines with calcium to form calcium phosphate, the bone mineral.
• Vitamin D helps the body absorb calcium and phosphorus. Lack of it also leads to rickets.

If a mother's diet lacks calcium and phosphorus, the baby's bones may not develop properly. They stay soft and bend under the child's weight once he begins to walk, which gives crooked legs.

Step 3: Check each option

• A. Sodium and iron: Sodium is for nerve impulses and water balance. Iron is for haemoglobin, and its lack causes anaemia. Not bone-related.
• B. Iron and manganese: Iron is for blood. Manganese is needed in small amounts for enzyme activity. Not the main bone minerals.
• C. Calcium and phosphorus: These are the main bone-building minerals. Correct.
• D. Magnesium and sulphur: Magnesium is for plant chlorophyll and has minor roles in bone. Sulphur is a component of proteins. Not the main cause.

Step 4: Answer The correct option is C. Calcium and phosphorus.

Exam tip: Link deficiencies to their effects:

• Calcium + phosphorus (and vitamin D) → rickets, weak bones and teeth
• Iron → anaemia
• Iodine → goitre
• Vitamin C → scurvy