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Which of the following pairs is correct in terms of pH values? (a) Tooth decay in humans: pH of mouth > 5.5 (b) pH range of human body: 7.0 to 7.8 (c) Acid rain: pH of rain water > 8
Only (b) is correct.
, (b) and (c) are correct.
Only (c) is correct.
Only (a) is correct.
Only (b) is correct.
The only factually correct statement is that the human body functions within a narrow pH range of 7.0 to 7.8. Tooth decay occurs when the mouth pH falls below 5.5, and acid rain is characterized by a pH significantly lower than 5.6, not greater than 8.
The only factually correct statement is that the human body functions within a narrow pH range of 7.0 to 7.8. Tooth decay occurs when the mouth pH falls below 5.5, and acid rain is characterized by a pH significantly lower than 5.6, not greater than 8.
Think of the human body's pH like a finely tuned thermostat; if it goes too high (alkalosis) or too low (acidosis), the 'engine' of the body struggles to function properly.
7-7.8 is our state; below 5.5, teeth seal their fate.
pH=тИТlog10тАЛ[H+] тАФ Definition of pH
Ca10тАЛ(PO4тАЛ)6тАЛ(OH)2тАЛ+8H+тЖТ10Ca2++6HPO42тИТтАЛ+2H2тАЛO тАФ Reaction of tooth enamel with acid
The human body maintains blood pH between 7.35 and 7.45 through buffer systems like bicarbonate/carbonic acid. Tooth enamel, primarily hydroxyapatite Ca10тАЛ(PO4тАЛ)6тАЛ(OH)2тАЛ, begins to dissolve (demineralization) when acidic conditions (pH<5.5) favor the release of H+ ions. Acid rain forms when sulfur dioxide (SO2тАЛ) or nitrogen oxides (NOxтАЛ) dissolve in atmospheric moisture to form sulfuric or nitric acid, leading to a pH typically between 4.0 and 5.0.
Human blood pH is strictly maintained between 7.35 and 7.45.
Tooth enamel starts demineralization below pH 5.5.
Normal rain has a pH of about 5.6 due to dissolved CO2тАЛ; acid rain is anything lower.
Biological homeostasis
Dental hygiene and fluoride treatment
Environmental monitoring of pollution
Option (a) is incorrect because tooth decay occurs when pH < 5.5.
Option (c) is incorrect because acid rain is acidic, meaning pH < 5.6, definitely not > 8 (which is basic).
B is correct тАФ The physiological pH range for the human body is approximately 7.0 to 7.8, which is essential for survival.
In competitive exams, remember that pH values below 7 are acidic, 7 is neutral, and above 7 are basic; always check the inequality signs carefully.
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