Knock knee syndrome is caused by-
Fluoride pollution
The correct option is A.
Explanation of the correct option:
Knock knee:
Causes of knock knee disease-
Fluoride poisoning:
Fluoride poisoning or pollution of fluoride means accumulation of fluoride inside the body which can cause the deficiency of vitamin D and thus, it might lead to knock knee syndrome.
Explanation of the incorrect options:
Option B:
Lead pollution: When an excess amount of lead gets deposited in our body it causes a delay in the growth and development, abdominal pain, neurological changes, etc.
Option C
Mercury pollution: Accumulation of mercury inside the body causes neurological damage, impaired motor skills, and other related issues.
Option D:
Arsenic pollution: Arsenic is extremely harmful to the body, its accumulation in the body mainly affects the liver, lungs, kidneys, and skin, it might also lead to coma or death.
Final answer: Knock knee syndrome is caused by fluoride pollution.