Q1. What substance has a pH value of 7, indicating neutrality?
a) Lemon juice
b) Vinegar
c) Pure water
d) Bleach
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Correct Answer: c) Pure water
Explanation: Pure water has a pH of 7, which is considered neutral. This means it has an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻). Substances with a pH below 7 are acidic, while those above 7 are basic or alkaline.
Q2. Which of the following substances has a pH value below 7?
a) Milk
b) Baking soda solution
c) Lemon juice
d) Soap solution
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Correct Answer: c) Lemon juice
Explanation: Lemon juice has a pH below 7, making it acidic. The acidity of lemon juice is primarily due to the presence of citric acid. Substances with a pH below 7 have a higher concentration of hydrogen ions (H⁺) than hydroxide ions (OH⁻).
Q3. What is the pH range of acidic substances on the pH scale?
a) 0-4
b) 5-7
c) 7-10
d) 11-14
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Correct Answer: a) 0-4
Explanation: Acidic substances have pH values ranging from 0 to 4 on the pH scale. The lower the pH value, the stronger the acid. Common acidic substances include lemon juice, vinegar, and stomach acid (gastric acid).
Q4. Which of the following is an example of a basic or alkaline substance?
a) Orange juice
b) Tomato juice
c) Bleach
d) Coffee
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Correct Answer: c) Bleach
Explanation: Bleach is a basic or alkaline substance with a pH value above 7. It typically has a pH ranging from 11 to 14. Basic substances have a higher concentration of hydroxide ions (OH⁻) than hydrogen ions (H⁺) and can feel slippery to the touch.
Q5. What is the pH of a solution that is considered highly acidic?
a) pH 3
b) pH 7
c) pH 9
d) pH 12
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Correct Answer: a) pH 3
Explanation: A solution with a pH of 3 is considered highly acidic. The pH scale is logarithmic, meaning each unit represents a tenfold change in acidity or alkalinity. Thus, a solution with a pH of 3 is ten times more acidic than one with a pH of 4.
Q6. Which substance is commonly used to neutralize acidic solutions?
a) Vinegar
b) Baking soda
c) Lemon juice
d) Hydrochloric acid
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Correct Answer: b) Baking soda
Explanation: Baking soda (sodium bicarbonate) is commonly used to neutralize acidic solutions due to its alkaline nature. When added to an acidic solution, baking soda reacts to produce water, carbon dioxide, and a salt, effectively raising the pH and neutralizing the acidity.
Q7. What is the pH of a solution that is considered basic?
a) pH 1
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 basic or alkaline. Basic solutions have a higher concentration of hydroxide ions (OH⁻) than hydrogen ions (H⁺). Common examples of basic substances include bleach, ammonia, and soapy water.
Q8. Which of the following substances has a pH value closest to neutral?
a) Battery acid
b) Tomato juice
c) Baking soda solution
d) Lemon juice
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Correct Answer: b) Tomato juice
Explanation: Tomato juice typically has a pH value close to neutral, around pH 4 to 4.5. While slightly acidic, it is less acidic than lemon juice or battery acid. Neutral substances have a pH of 7, indicating an equal concentration of hydrogen ions and hydroxide ions.
Q9. What pH range characterizes basic or alkaline substances on the pH scale?
a) 0-4
b) 5-7
c) 7-10
d) 11-14
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Correct Answer: d) 11-14
Explanation: Basic or alkaline substances have pH values ranging from 11 to 14 on the pH scale. The higher the pH value, the stronger the base. Examples of basic substances include bleach, ammonia, and oven cleaner.
Q10. Which of the following is an example of a substance with a pH value of 1?
a) Orange juice
b) Battery acid
c) Milk
d) Coffee
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Correct Answer: b) Battery acid
Explanation: Battery acid typically has a pH value of 1, making it highly acidic. It contains sulfuric acid, which is corrosive and can cause severe burns upon contact with skin. Substances with pH values of 1 are considered extremely acidic.