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Tooth decay starts when the pH of the mouth is lower than 5.5.
When pH of rain water is more than 5.6, it is called acid rain.
Living organisms can survive only in a narrow range of pH change.
When pH of rain water is more than 5.6, it is called acid rain.
Acid rain is defined as precipitation (rain, snow, fog, etc.) that is unusually acidic, meaning it possesses elevated levels of hydrogen ions (pH levels). Pure rainwater is slightly acidic (around pH 5.6) due to dissolved carbon dioxide forming weak carbonic acid. When the pH of rain water falls below 5.6, it is categorized as acid rain.
Acid rain is defined as precipitation (rain, snow, fog, etc.) that is unusually acidic, meaning it possesses elevated levels of hydrogen ions (pH levels). Pure rainwater is slightly acidic (around pH 5.6) due to dissolved carbon dioxide forming weak carbonic acid. When the pH of rain water falls below 5.6, it is categorized as acid rain.
Just like adding lemon juice (acid) to pure water lowers its pH and makes it sour, industrial emissions release acidic gases into clouds, making rainwater acidic.
SOтВВ and NO bring acid rain low (pH<5.6).
pH=тИТlog10тАЛ[H+] тАФ Definition of pH
CO2тАЛ+H2тАЛOтЗМH2тАЛCO3тАЛ тАФ Carbonic acid formation in normal rain
Human activities emit sulfur dioxide (SO2тАЛ) and nitrogen oxides (NOxтАЛ) into the atmosphere from burning fossil fuels. These gases react with water vapor, oxygen, and other chemicals in the atmosphere to form sulfuric acid (H2тАЛSO4тАЛ) and nitric acid (HNO3тАЛ), which then fall to the ground as precipitation, lowering the pH below 5.6.
Normal clean rainwater has a pH of approximately 5.6 due to atmospheric carbon dioxide.
Rainwater with a pH less than 5.6 is designated as acid rain.
Acid rain is primarily caused by sulfur dioxide (SO2тАЛ) and nitrogen oxides (NOxтАЛ) reacting with atmospheric moisture.
Living organisms and aquatic life (like fish) suffer severely when water bodies become acidic.
Environmental monitoring of industrial pollution
Agricultural soil management using lime to neutralize acidity
Option A is correct: Tooth decay starts when mouth pH drops below 5.5 due to acid production by bacteria.
Option B is correct: Rain water is termed acid rain when its pH is less than 5.6.
Option C is correct: Biological systems (such as the human body) operate within a tightly controlled pH range of 7.0 to 7.8.
Option D is INCORRECT because acid rain occurs when pH is less than 5.6, not more than 5.6.
D is correct тАФ When pH of rain water is more than 5.6, it is called acid rain is an incorrect statement as acid rain is defined when pH is less than 5.6.
Remember that pH values below 7 are acidic, 7 is neutral, and above 7 are basic. For exam questions on acid rain, always remember the threshold limit of 5.6.
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