📌 How to Use
First read the questions carefully using the Read section. Use the Details button to understand concepts clearly. After completing reading, click Practice Quiz to test yourself.
📘 Study MCQs
Q1. Phenolphthalein is a synthetic indicator. What color does it turn when added to a basic solution like sodium hydroxide? SCIENCE
• Yellow
• Red
• Pink
• Green
Answer: Pink
Phenolphthalein is a colorless liquid in acidic and neutral solutions. However, when added to a basic solution, it turns a distinct pink or magenta color.
Q2. A student adds a few drops of phenolphthalein to a solution of hydrochloric acid. What color change will he observe? SCIENCE
• Colorless to pink
• Pink to colorless
• Remains colorless
• Colorless to red
Answer: Remains colorless
Phenolphthalein remains colorless in acidic solutions. Since hydrochloric acid is an acid, the phenolphthalein will show no color change and the solution will stay colorless.
Q3. A student adds phenolphthalein to a colorless solution, and it turns pink. What is the nature of the solution? SCIENCE
• Acidic
• Neutral
• Basic
• Slightly sour
Answer: Basic
Phenolphthalein is an indicator that specifically turns pink in basic (alkaline) solutions. If the solution turns pink, it confirms the presence of a base.
Q4. Limewater is a basic solution. If a few drops of phenolphthalein are added to it, what will happen? SCIENCE
• The solution will become colorless
• The solution will turn pink
• The solution will turn red
• The solution will turn blue
Answer: The solution will turn pink
Limewater (calcium hydroxide) is a base. Phenolphthalein turns pink in the presence of a base, so the limewater will change to a pink color.
Q5. Generally, acids have a specific taste. What is that taste? SCIENCE
• Sweet
• Bitter
• Sour
• Salty
Answer: Sour
One of the general physical properties of acids is that they have a sour taste. This is why substances like lemon (citric acid) and vinegar (acetic acid) taste sour.
Q6. How do dilute acids generally feel when touched? (With a warning that this should never be tested directly) SCIENCE
• Soapy and slippery
• Sticky
• No specific feeling
• Watery
Answer: No specific feeling
Unlike bases which feel soapy or slippery, dilute acids generally feel like water. However, strong acids are corrosive and should never be touched.
Q7. Which gas is usually produced when an acid reacts with an active metal like zinc? SCIENCE
• Oxygen
• Carbon dioxide
• Hydrogen
• Nitrogen
Answer: Hydrogen
When acids react with active metals, they produce hydrogen gas. This can be tested by bringing a burning splint near it, which will put out with a ‘pop’ sound.
Q8. Acid rain is a environmental problem. What is the main cause of acid rain? SCIENCE
• Excessive use of fertilizers
• Burning of fossil fuels releasing oxides of sulphur and nitrogen
• Deforestation
• Use of air conditioners
Answer: Burning of fossil fuels releasing oxides of sulphur and nitrogen
Power plants, factories, and vehicles burn fossil fuels (coal and petrol) which release sulphur dioxide and nitrogen oxides. These gases mix with rain water to form sulphuric acid and nitric acid, causing acid rain.
Q9. What is the approximate pH of normal rain water? SCIENCE
• Below 5.6
• Around 5.6
• Exactly 7
• Above 8
Answer: Around 5.6
Normal rain water is slightly acidic because it absorbs carbon dioxide from the air to form weak carbonic acid. Its pH is around 5.6. Rain with a pH lower than 5.6 is considered acid rain.
Q10. Acid rain can cause damage to buildings made of which material? SCIENCE
• Wood
• Plastic
• Marble (Calcium carbonate)
• Glass
Answer: Marble (Calcium carbonate)
Marble is made of calcium carbonate, which reacts with the acids in acid rain. This reaction causes the marble to corrode and wear away, a process known as “stone cancer” seen on historical monuments like the Taj Mahal.
Q11. What is the chemical process called when an acid and a base react to form salt and water? SCIENCE
• Polymerization
• Oxidation
• Neutralization
• Precipitation
Answer: Neutralization
The reaction between an acid and a base is known as neutralization. In this reaction, the acidic and basic properties cancel each other out to form a salt and water as products.
Q12. A person suffers from indigestion due to excess acid in the stomach. What type of substance is taken to relieve this pain? SCIENCE
• Acidic substance
• Basic substance (antacid)
• Neutral substance
• Sour substance
Answer: Basic substance (antacid)
Indigestion is caused by excess hydrochloric acid in the stomach. To neutralize this excess acid, a person takes an antacid, which contains mild bases like magnesium hydroxide or sodium hydrogen carbonate.
Q13. Milk of Magnesia is often used as an antacid. Which base does it contain? SCIENCE
• Sodium hydroxide
• Calcium hydroxide
• Magnesium hydroxide
• Ammonium hydroxide
Answer: Magnesium hydroxide
Milk of Magnesia is the common name for a suspension of magnesium hydroxide, Mg(OH)₂. It is a mild base that neutralizes excess stomach acid without being harmful.
Q14. Baking soda is a common home remedy for acidity. What is its chemical name? SCIENCE
• Sodium chloride
• Sodium carbonate
• Sodium hydrogen carbonate
• Calcium carbonate
Answer: Sodium hydrogen carbonate
Baking soda is sodium hydrogen carbonate (NaHCO₃). It is a mild base that can quickly neutralize excess acid in the stomach, providing relief from acidity.
Q15. Farmers add slaked lime to their fields. What is the purpose of this practice? SCIENCE
• To add more acid to the soil
• To make the soil more fertile by adding nutrients
• To treat soil that is too acidic (basic soil treatment)
• To kill insects
Answer: To treat soil that is too acidic (basic soil treatment)
If the soil becomes too acidic, it is not good for plant growth. Farmers add a base like slaked lime (calcium hydroxide) or quicklime to the soil to neutralize the excess acid. This process is called soil treatment.
Q16. Sometimes farmers add organic matter (compost) to the soil. This can also help treat soil that is too ______. SCIENCE
• Basic (alkaline)
• Sandy
• Dry
• Rocky
Answer: Basic (alkaline)
If soil is too basic (alkaline), it is not suitable for crops. Organic matter (compost) releases acids when it decomposes, which helps to neutralize the excess base in the soil.
Q17. Waste from factories is often acidic. Why is it dangerous to dump this waste directly into rivers? SCIENCE
• It will change the color of the river
• It will kill aquatic life by making the water acidic
• It will make the river water salty
• It will cause the river to freeze
Answer: It will kill aquatic life by making the water acidic
Aquatic plants and animals can only survive in a narrow pH range. If acidic factory waste is dumped into rivers, it lowers the pH of the water, making it too acidic for fish and other organisms to survive.
Q18. How is acidic factory waste treated before being released into water bodies? SCIENCE
• By diluting it with large amounts of water
• By adding a base to neutralize it
• By boiling it
• By filtering it
Answer: By adding a base to neutralize it
Factory waste is treated in special plants where it is neutralized. A basic substance, like calcium hydroxide (lime), is added to the acidic waste. The acid and base react, neutralizing the waste to a safe pH level.
Q19. When an ant stings a person, it injects a liquid into the skin. What is the nature of this liquid? SCIENCE
• Basic
• Neutral
• Acidic
• Salty
Answer: Acidic
An ant sting injects methanoic acid (also known as formic acid) into the skin. This acid causes the pain and irritation.
Q20. What is a common household remedy to apply on an ant sting to get relief? SCIENCE
• Lemon juice
• Vinegar
• Baking soda paste
• Common salt
Answer: Baking soda paste
Since an ant sting is acidic, a mild base is used to neutralize it. Baking soda (sodium hydrogen carbonate) mixed with water to form a paste is a basic substance that neutralizes the methanoic acid, providing relief.
Q21. A bee sting is different from an ant sting. What is the nature of the liquid injected by a bee sting? SCIENCE
• Acidic
• Basic
• Neutral
• Sour
Answer: Basic
While ant stings are acidic, bee stings are basic in nature. They inject an alkaline liquid that causes pain and swelling.
Q22. What can be used to treat a bee sting? SCIENCE
• Baking soda paste
• Lemon juice or vinegar
• Soap solution
• Sugar solution
Answer: Lemon juice or vinegar
Since a bee sting is basic, it needs to be neutralized by a mild acid. Applying a weak acid like lemon juice (citric acid) or vinegar (acetic acid) can help neutralize the basic venom and reduce the pain.
Q23. Why is it important to know whether a sting is from an ant or a bee before applying a remedy? SCIENCE
• Because ants are more dangerous
• Because one is acidic and the other is basic, so they need opposite treatments
• Because the remedies smell different
• Because the sting location is different
Answer: Because one is acidic and the other is basic, so they need opposite treatments
Ant stings are acidic (requiring a base for treatment), while bee stings are basic (requiring an acid for treatment). Using the wrong remedy could worsen the irritation instead of neutralizing it.
Q24. In very hot weather, milk spoils quickly and becomes sour. Why does this happen? SCIENCE
• The heat kills the bacteria
• Bacteria convert the milk sugar (lactose) into lactic acid
• The milk evaporates
• The fat separates from the milk
Answer: Bacteria convert the milk sugar (lactose) into lactic acid
In warm conditions, bacteria in milk multiply rapidly. These bacteria feed on lactose (milk sugar) and convert it into lactic acid. This acid makes the milk taste sour and causes it to curdle.
Q25. To preserve milk for a short period, especially in warm weather, people often boil it. Why does boiling help? SCIENCE
• It adds nutrients to the milk
• It kills the bacteria that turn milk sour
• It makes the milk sweeter
• It removes all the water
Answer: It kills the bacteria that turn milk sour
Boiling milk kills the bacteria present in it. With the bacteria gone, they cannot convert the lactose into lactic acid, so the milk stays fresh for a longer period.
Q26. A student accidentally spills dilute hydrochloric acid on the laboratory floor. The teacher instructs her to neutralize it with a base. Which substance would be safest to use? SCIENCE
• Concentrated sodium hydroxide
• Water
• Baking soda (sodium hydrogen carbonate)
• Sulphuric acid
Answer: Baking soda (sodium hydrogen carbonate)
Baking soda is a mild, safe base that can be used to neutralize acid spills. It reacts with the acid to form salt and water, making the spill safe to clean up. Strong bases like NaOH would be dangerous.
Q27. What will be the products when an acid reacts with a base in a neutralization reaction? SCIENCE
• A new acid and a new base
• Carbon dioxide and water
• Salt and water
• Hydrogen gas and salt
Answer: Salt and water
The general equation for a neutralization reaction is: Acid + Base → Salt + Water. For example, HCl + NaOH → NaCl (salt) + H₂O (water).
Q28. Why is it not advisable to take antacid tablets regularly without a doctor’s advice? SCIENCE
• They are too expensive
• They can make the stomach too basic, affecting digestion
• They taste bad
• They are difficult to swallow
Answer: They can make the stomach too basic, affecting digestion
Our stomach needs a specific acidic environment for enzymes to work properly and digest food. Taking too many antacids can neutralize too much acid, making the stomach too basic and interfering with the digestive process.
Q29. Besides using a base, how can the effects of acid rain on a lake be reduced? SCIENCE
• By adding more acid to the lake
• By adding a basic substance like lime (calcium hydroxide) to the lake
• By boiling the lake water
• By filtering the lake water
Answer: By adding a basic substance like lime (calcium hydroxide) to the lake
If a lake becomes too acidic due to acid rain, powdered limestone (calcium carbonate) or lime (calcium hydroxide) can be added. This base neutralizes the excess acid in the lake water, restoring a pH level that can support aquatic life.
Q30. A solution turns phenolphthalein pink. When an acid is added to it drop by drop, what will happen to the pink color? SCIENCE
• It will become darker pink
• It will turn blue
• It will become colorless
• It will turn yellow
Answer: It will become colorless
The pink color of phenolphthalein in a base is due to the presence of OH⁻ ions. When acid (H⁺ ions) is added, neutralization occurs. As the base is used up, the solution becomes neutral, and the phenolphthalein returns to its colorless form.