Q1. What does the pH scale measure?
a) Temperature
b) Acidity or alkalinity
c) Pressure
d) Density
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Correct Answer: b) Acidity or alkalinity
Explanation: The pH scale is a measure of the acidity or alkalinity of a solution. It quantifies the concentration of hydrogen ions (H⁺) in a solution, which determines its acidity or alkalinity.
Q2. Which of the following substances would have a pH value below 7?
a) Lemon juice
b) Baking soda solution
c) Soap solution
d) Milk
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Correct Answer: a) Lemon juice
Explanation: Lemon juice is acidic in nature due to the presence of citric acid, which gives it a sour taste. Citric acid releases hydrogen ions (H⁺) when dissolved in water, resulting in a solution with a pH below 7. Thus, lemon juice would have a pH value below 7 on the pH scale, indicating its acidity.
Q3. What does a pH value of 7 indicate on the pH scale?
a) Strong acidity
b) Strong alkalinity
c) Neutrality
d) Weak acidity
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Correct Answer: c) Neutrality
Explanation: A pH value of 7 indicates neutrality on the pH scale. In a neutral solution, the concentration of hydrogen ions (H⁺) is equal to the concentration of hydroxide ions (OH⁻), resulting in a balanced state. Pure water at 25°C has a pH of 7, as it contains an equal number of hydrogen ions and hydroxide ions, making it neither acidic nor alkaline.
Q4. Which of the following substances would have a pH value above 7?
a) Vinegar
b) Lemon juice
c) Ammonia solution
d) Orange juice
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Correct Answer: c) Ammonia solution
Explanation: Ammonia solution is alkaline in nature due to the presence of ammonia (NH₃), which acts as a base.
Q5. Which of the following substances is considered neutral on the pH scale?
a) Battery acid
b) Bleach solution
c) Pure water
d) Hydrochloric acid
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Correct Answer: c) Pure water
Explanation: Pure water is considered neutral on the pH scale, with a pH value of 7. At 25°C, pure water contains an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻), resulting in a balanced state of acidity and alkalinity. Therefore, pure water neither exhibits acidic nor alkaline properties, making it neutral. In contrast, battery acid (a) and hydrochloric acid (d) are highly acidic, while bleach solution (b) is alkaline.
Q6. Which of the following pH values indicates a strongly acidic solution?
a) pH 4
b) pH 7
c) pH 9
d) pH 12
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Correct Answer: a) pH 4
Explanation: A pH value of 4 indicates a strongly acidic solution on the pH scale. Solutions with pH values below 7 are acidic, and the lower the pH value, the higher the acidity. Therefore, pH 4 represents a higher concentration of hydrogen ions (H⁺) compared to pH 7, indicating stronger acidity. In contrast, pH 7 is neutral, pH 9 is alkaline, and pH 12 indicates a strongly alkaline solution.
Q7. What pH value represents a solution with strong alkalinity?
a) pH 1
b) pH 7
c) pH 9
d) pH 5
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Correct Answer: c) pH 9
Explanation: A pH value of 9 represents a solution with strong alkalinity on the pH scale. Solutions with pH values above 7 are alkaline or basic, and the higher the pH value, the stronger the alkalinity. Therefore, pH 9 indicates a higher concentration of hydroxide ions (OH⁻) compared to pH 7, indicating strong alkalinity. In contrast, pH 1 is strongly acidic, pH 7 is neutral, and pH 5 is weakly acidic.
Q8. Which of the following substances would have a pH value closest to that of human blood?
a) Lemon juice
b) Vinegar
c) Ammonia solution
d) Saline solution
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Correct Answer: d) Saline solution
Explanation: Saline solution, which is a solution of sodium chloride (NaCl) in water, typically has a pH value closest to that of human blood, which is around 7.35 to 7.45. Saline solution is commonly used in medical settings, such as intravenous fluids and wound irrigation, due to its isotonic nature, which means it has a similar osmotic pressure to bodily fluids. Lemon juice (a) and vinegar (b) are acidic, while ammonia solution (c) is alkaline, and their pH values are not comparable to that of human blood.
Q9. Which of the following substances is commonly used to adjust the pH of soil in gardening and agriculture?
a) Lemon juice
b) Ammonia solution
c) Lime
d) Vinegar
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Correct Answer: c) Lime
Explanation: Lime, particularly agricultural lime or calcium carbonate (CaCO3), is commonly used to adjust the pH of soil in gardening and agriculture.
Q10. Which of the following statements about the pH scale is correct?
a) A lower pH value indicates stronger alkalinity.
b) A pH value of 7 indicates strong acidity.
c) The pH scale ranges from 0 to 10.
d) pH stands for “Potential of Hydrocarbons.”
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Correct Answer: c) The pH scale ranges from 0 to 14.
Explanation: The pH scale is a logarithmic scale that ranges from 0 to 14, with 7 representing neutrality. A pH value below 7 indicates acidity, with lower pH values indicating stronger acidity. Conversely, pH values above 7 indicate alkalinity or basicity, with higher pH values indicating stronger alkalinity.