Q11. What is the pH of a solution that is neither acidic nor basic?
a) pH 1
b) pH 7
c) pH 9
d) pH 14
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Correct Answer: b) pH 7
Explanation: A solution with a pH of 7 is considered neutral. This means it has an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻), resulting in a balanced pH. Pure water at room temperature is an example of a neutral solution.
Q12. Which substance is commonly used to lower the pH of soil for plants that prefer acidic conditions?
a) Lime
b) Vinegar
c) Ammonia
d) Sulfur
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Correct Answer: d) Sulfur
Explanation: Sulfur is commonly used to lower the pH of soil for plants that prefer acidic conditions, a process known as acidification. When sulfur is added to soil, it undergoes oxidation to form sulfuric acid, which gradually lowers the soil pH.
Q13. What pH range characterizes neutral substances on the pH scale?
a) 0-4
b) 5-7
c) 7-10
d) 11-14
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Correct Answer: b) 5-7
Explanation: Neutral substances have pH values ranging from 5 to 7 on the pH scale. A pH of 7 is considered completely neutral, indicating a balanced concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻). Pure water at room temperature is an example of a neutral substance.
Q14. Which of the following substances is commonly used to raise the pH of acidic soil?
a) Vinegar
b) Lemon juice
c) Ammonia
d) Battery acid
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Correct Answer: c) Ammonia
Explanation: Ammonia is commonly used to raise the pH of acidic soil for plants that prefer alkaline conditions. It acts as a base and reacts with soil acids to form ammonium ions (NH₄⁺), which increase the soil’s pH.
Q15. What is the pH value of a substance that is considered moderately acidic?
a) pH 3
b) pH 7
c) pH 9
d) pH 11
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Correct Answer: a) pH 3
Explanation: A substance with a pH of 3 is considered moderately acidic. pH values between 0 and 6.9 are classified as acidic, with lower values indicating stronger acidity. Common moderately acidic substances include orange juice and soda.
Q16. Which of the following substances is commonly used to increase the pH of swimming pool water?
a) Lemon juice
b) Vinegar
c) Baking soda
d) Hydrochloric acid
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Correct Answer: c) Baking soda
Explanation: Baking soda (sodium bicarbonate) is commonly used to increase the pH of swimming pool water, which tends to become acidic due to the addition of chlorine. Baking soda acts as a buffer, helping to maintain the pool water’s pH within the ideal range.
Q17. What is the pH of a solution that is considered highly basic?
a) pH 3
b) pH 7
c) pH 9
d) pH 12
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Correct Answer: d) pH 12
Explanation: A solution with a pH of 12 is considered highly basic or alkaline. Basic solutions have a higher concentration of hydroxide ions (OH⁻) than hydrogen ions (H⁺). Substances with pH values above 7 are classified as basic.
Q18. Which of the following substances is commonly used to test the pH of solutions?
a) Litmus paper
b) Salt
c) Sugar
d) Aluminum foil
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Correct Answer: a) Litmus paper
Explanation: Litmus paper is commonly used to test the pH of solutions. It contains a mixture of dyes that change color depending on the acidity or alkalinity of the solution being tested. Blue litmus paper turns red in acidic solutions and red litmus paper turns blue in basic solutions.
Q19. What is the pH of a solution that is considered weakly acidic?
a) pH 2
b) pH 7
c) pH 8
d) pH 10
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Correct Answer: a) pH 2
Explanation: A solution with a pH of 2 is considered weakly acidic. pH values between 0 and 6.9 are classified as acidic, with lower values indicating stronger acidity. Examples of weakly acidic substances include coffee and vinegar.
Q20. Which of the following substances is commonly used to measure the pH of soil?
a) pH meter
b) Litmus paper
c) Soil probe
d) Hydrometer
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Correct Answer: a) pH meter
Explanation: A pH meter is commonly used to measure the pH of soil. It consists of a probe that is inserted into the soil to directly measure the pH value. pH meters provide more accurate and precise measurements compared to other methods such as using litmus paper or soil probes.