📌 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. The word ‘acid’ comes from the Latin word ‘acidus’. What is the meaning of ‘acidus’? SCIENCE
• Sweet
• Bitter
• Sour
• Salty
Answer: Sour
The Latin word ‘acidus’ literally means sour. This is because many acidic substances, like lemon juice and vinegar, have a sour taste.
Q2. Which of the following is a natural acid found in curd? SCIENCE
• Citric acid
• Tartaric acid
• Acetic acid
• Lactic acid
Answer: Lactic acid
Curd is formed by the action of bacteria on milk. These bacteria convert the natural sugars in milk into lactic acid, which gives curd its characteristic sour taste.
Q3. Vinegar is a common substance in our kitchens. Which acid is present in it? SCIENCE
• Citric acid
• Tartaric acid
• Acetic acid
• Oxalic acid
Answer: Acetic acid
Vinegar is essentially a dilute solution of acetic acid. It is this acid that gives vinegar its sharp, sour flavor and pungent smell.
Q4. Lemons and oranges taste sour because they contain a specific acid. What is it? SCIENCE
• Lactic acid
• Citric acid
• Tartaric acid
• Ascorbic acid
Answer: Citric acid
Citrus fruits like lemons, oranges, and grapes are rich in citric acid. This natural acid is responsible for their tangy and refreshing sour taste.
Q5. Tamarind is used as a souring agent in many Indian dishes. Which acid gives it this sour taste? SCIENCE
• Citric acid
• Lactic acid
• Tartaric acid
• Acetic acid
Answer: Tartaric acid
The sour taste of tamarind pulp is due to the presence of tartaric acid. It is a natural acid also found in grapes and is a key ingredient in some baking powders.
Q6. What is the general name for acids that are obtained from natural sources like plants and animals? SCIENCE
• Mineral acids
• Strong acids
• Organic acids
• Weak acids
Answer: Organic acids
Acids derived from living organisms, such as plants (citric acid) and animals (lactic acid from milk), are known as organic acids. They are usually not very strong.
Q7. Acids that are prepared from minerals of the earth are called mineral acids. Which of these is a mineral acid? SCIENCE
• Citric acid
• Lactic acid
• Acetic acid
• Sulphuric acid
Answer: Sulphuric acid
Sulphuric acid is manufactured from chemical elements found in minerals. It is a strong mineral acid, unlike organic acids which come from natural sources like plants.
Q8. Queen of Chemicals SCIENCE
• King of Chemicals
Answer: King of Chemicals
Sulphuric acid is used in the manufacturing of everything from fertilizers and paints to detergents and fibres. Because of its widespread and vital use in industry, it is called the ‘King of Chemicals’.
Q9. Nitric acid is another important mineral acid. In which of the following processes is it commonly used? SCIENCE
• Making soaps
• Manufacturing of fertilizers
• Cooking food
• Making window cleaners
Answer: Manufacturing of fertilizers
Nitric acid is a key ingredient in the production of many common fertilizers, such as ammonium nitrate, which are essential for healthy plant growth.
Q10. Our stomach produces a mineral acid to help digest food. Which acid is this? SCIENCE
• Sulphuric acid
• Nitric acid
• Phosphoric acid
• Hydrochloric acid
Answer: Hydrochloric acid
The gastric juices in our stomach contain dilute hydrochloric acid (HCl). This acid helps to break down food and kill any harmful bacteria that might be ingested.
Q11. Phosphoric acid is often used to add a tangy flavor to soft drinks. What is its chemical formula? SCIENCE
• HCl
• H₂SO₄
• HNO₃
• H₃PO₄
Answer: H₃PO₄
The chemical formula for phosphoric acid is H₃PO₄. It is a mineral acid that not only adds flavor but also helps prevent the growth of mold and bacteria in soft drinks.
Q12. Which type of acids are the building blocks of fats and oils? SCIENCE
• Amino acids
• Nucleic acids
• Fatty acids
• Mineral acids
Answer: Fatty acids
Fats and oils are made up of smaller units called fatty acids. Examples include oleic acid (in olive oil) and palmitic acid (in palm oil).
Q13. Proteins are made up of smaller units. What are these units called? SCIENCE
• Fatty acids
• Amino acids
• Sulphuric acid
• Nucleic acids
Answer: Amino acids
Just as a wall is made of bricks, proteins are made of small units called amino acids. There are 20 different types of amino acids that combine in different ways to form all the proteins our body needs.
Q14. The molecule that carries our genetic information is called DNA. What type of acid is DNA? SCIENCE
• Fatty acid
• Amino acid
• Mineral acid
• Nucleic acid
Answer: Nucleic acid
DNA stands for Deoxyribonucleic Acid. It is a type of nucleic acid, which is a family of large molecules responsible for storing and transmitting genetic information in living beings.
Q15. Soap is a common substance we use for bathing. What is the nature of a soap solution? SCIENCE
• Acidic
• Basic
• Neutral
• Slightly sour
Answer: Basic
Soaps are salts formed from a reaction between a base and a fat. When dissolved in water, they create a basic (alkaline) solution, which helps in cleaning.
Q16. Liquid soap often contains a base that is also found in window cleaners. Which base is this? SCIENCE
• Sodium hydroxide
• Calcium hydroxide
• Magnesium hydroxide
• Potassium hydroxide
Answer: Potassium hydroxide
Potassium hydroxide (KOH) is a strong base. Its chemical properties make it effective in liquid soaps and also in cleaning solutions like window cleaners.
Q17. A white solid is used for whitewashing walls. When mixed with water, it forms limewater. What is this substance? SCIENCE
• Sodium hydroxide
• Calcium hydroxide
• Magnesium hydroxide
• Ammonium hydroxide
Answer: Calcium hydroxide
The substance used for whitewashing is calcium hydroxide, Ca(OH)₂. A solution of this compound in water is called limewater, which is used to test for carbon dioxide.
Q18. Doctors prescribe ‘Milk of Magnesia’ to relieve acidity or indigestion. What is its chemical name? SCIENCE
• Calcium hydroxide
• Sodium hydroxide
• Magnesium hydroxide
• Ammonium hydroxide
Answer: Magnesium hydroxide
Milk of Magnesia is the common name for a suspension of magnesium hydroxide, Mg(OH)₂, in water. It is a base that neutralizes excess acid in the stomach.
Q19. A base is used in the manufacturing of soaps and is a key ingredient in drain cleaners. Its chemical formula is NaOH. What is its common name? SCIENCE
• Potassium hydroxide
• Calcium hydroxide
• Sodium hydroxide
• Ammonium hydroxide
Answer: Sodium hydroxide
The compound with the formula NaOH is sodium hydroxide. It is also known as caustic soda and is a very strong base used in many industrial processes.
Q20. Many window cleaning solutions contain a base with the formula NH₄OH. What is its chemical name? SCIENCE
• Sodium hydroxide
• Calcium hydroxide
• Magnesium hydroxide
• Ammonium hydroxide
Answer: Ammonium hydroxide
NH₄OH is the chemical formula for ammonium hydroxide. It is formed when ammonia gas dissolves in water and is effective at cutting through grease on glass surfaces.
Q21. What is the general name for a substance, like litmus or turmeric, that changes color to show whether a solution is acidic or basic? SCIENCE
• Indicator
• Catalyst
• Reagent
• Solvent
Answer: Indicator
Substances that change color in the presence of acids or bases are called indicators. They help us identify the chemical nature of a solution.
Q22. Litmus is a natural dye extracted from a plant. What is its original color? SCIENCE
• Red
• Blue
• Purple
• Green
Answer: Purple
Litmus is a purple dye extracted from lichens. It is a very useful indicator because it turns red in acidic solutions and blue in basic solutions.
Q23. A student adds a drop of a liquid to a red litmus paper. The paper turns blue. What is the nature of the liquid? SCIENCE
• Acidic
• Basic
• Neutral
• Sour
Answer: Basic
Red litmus paper is used to test for bases. If a base is present, the red litmus paper will change its color to blue. Acids do not change the color of red litmus.
Q24. A student adds a drop of a liquid to a blue litmus paper. The paper turns red. What is the nature of the liquid? SCIENCE
• Acidic
• Basic
• Neutral
• Soapy
Answer: Acidic
Blue litmus paper is used to test for acids. If an acid is present, the blue litmus paper will change its color to red. Bases do not change the color of blue litmus.
Q25. A solution is tested with both red and blue litmus papers, and neither paper changes color. What is the solution? SCIENCE
• Acidic
• Basic
• Neutral
• Can’t say
Answer: Neutral
If a solution is neutral (neither acidic nor basic), like pure water, it will not change the color of either red or blue litmus paper. Both papers remain the same color.
Q26. Soap solution turns the color of ______ litmus paper to blue. SCIENCE
• Blue
• Red
• Green
• Yellow
Answer: Red
Soap solution is basic. A basic solution turns red litmus paper blue. It does not change the color of blue litmus paper.
Q27. What effect does lemon juice, an acid, have on blue litmus paper? SCIENCE
• Turns it blue
• Turns it red
• No change
• Turns it green
Answer: Turns it red
Lemon juice is acidic. An acidic solution turns blue litmus paper red. It does not change the color of red litmus paper.
Q28. Turmeric is a natural indicator used in Indian kitchens. Its paste is yellow. What color does it turn when a basic solution like soap is added to it? SCIENCE
• Yellow
• Green
• Red
• Blue
Answer: Red
Turmeric is a natural indicator. It remains yellow in acidic and neutral solutions. However, when it comes in contact with a basic substance like soap, it turns reddish-brown.
Q29. A woman’s white saree gets a yellow stain of turmeric during a festival. Later, while washing, her soapy hands accidentally rub the stain. What will happen to the stain? SCIENCE
• It will become darker red
• It will disappear completely
• It will turn green
• Nothing will happen
Answer: It will become darker red
Soap is basic. When the basic soap comes in contact with the yellow turmeric stain, it will act as an indicator and turn the stain to a reddish-brown color, making it appear darker.
Q30. China rose is an indicator. Its solution is generally ______ in color. SCIENCE
• Red
• Yellow
• Green
• Light pink or magenta
Answer: Light pink or magenta
An indicator is prepared by boiling the petals of the China rose (Hibiscus) flower in water. The resulting solution is usually light pink or magenta in color.
Q31. When an acid is added to a China rose indicator, what color change is observed? SCIENCE
• Green
• Dark pink (Magenta)
• Yellow
• Blue
Answer: Dark pink (Magenta)
China rose indicator turns acidic solutions to a dark pink (or magenta) color. This is a clear visual distinction from its original light pink color.
Q32. When a base is added to a China rose indicator, what color change is observed? SCIENCE
• Dark pink (Magenta)
• Green
• Red
• No change
Answer: Green
China rose indicator is excellent for testing bases, as it turns basic solutions to a bright green color. This is very different from the color it shows for acids.
Q33. You have a China rose indicator (magenta color). You add it to a sample of tap water and the color changes to green. What does this tell you about the tap water? SCIENCE
• It is acidic
• It is basic
• It is neutral
• It is pure
Answer: It is basic
Since the China rose indicator turned green, this indicates that the tap water is basic in nature. This could be due to dissolved minerals or salts in the water.
Q34. Which of the following is NOT a natural indicator? SCIENCE
• Litmus
• Turmeric
• Phenolphthalein
• China rose
Answer: Phenolphthalein
Phenolphthalein is a chemical compound made in a laboratory. It is a synthetic indicator. Litmus, turmeric, and China rose are all obtained from natural sources (plants).
Q35. A substance tastes sour and turns blue litmus red. It is likely to be ______. SCIENCE
• Lemon juice
• Soap
• Baking soda
• Water
Answer: Lemon juice
Acids have a sour taste and turn blue litmus paper red. Among the options, only lemon juice is an acid. Soap and baking soda are basic, and water is neutral.
Q36. A substance feels soapy to touch and turns red litmus blue. It is likely to be ______. SCIENCE
• Vinegar
• Orange juice
• Soap solution
• Lemon juice
Answer: Soap solution
Bases feel soapy or slippery to the touch and turn red litmus paper blue. Soap solution is a base. Vinegar, orange, and lemon juice are all acids.
Q37. What is the nature of a substance that does not change the color of either red or blue litmus paper? SCIENCE
• Acidic
• Basic
• Neutral
• Sour
Answer: Neutral
Substances that are neither acidic nor basic are called neutral. Examples include pure water and sugar solution. They do not affect the color of litmus paper.
Q38. Which of the following eatable substances contains oxalic acid? SCIENCE
• Lemon
• Vinegar
• Tomato
• Spinach
Answer: Spinach
While tomatoes contain citric acid, spinach is a good source of oxalic acid. This natural organic acid is also found in rhubarb and sorrel.
Q39. What type of acid is ascorbic acid, which is commonly known as Vitamin C? SCIENCE
• Mineral acid
• Organic acid
• Strong acid
• Fatty acid
Answer: Organic acid
Ascorbic acid (Vitamin C) is found naturally in fruits and vegetables like oranges, lemons, and amla. Since it is derived from natural sources, it is classified as an organic acid.
Q40. The image shows a bottle of a soft drink. Which acid, besides carbonic acid, is commonly found in these drinks to give them a tangy flavor? SCIENCE
• Lactic acid
• Tartaric acid
• Phosphoric acid
• Acetic acid
Answer: Phosphoric acid
Many carbonated soft drinks contain phosphoric acid (H₃PO₄). It provides a tangy or sharp flavor and acts as a preservative.
Q41. A gardener wants to reduce the acidity of his garden soil. Which substance should he add? SCIENCE
• Vinegar
• Lemon juice
• Lime (Calcium hydroxide)
• Water
Answer: Lime (Calcium hydroxide)
To reduce soil acidity (i.e., make it less acidic and more basic), gardeners add a base like lime, which is calcium hydroxide. This process is called ‘liming’.
Q42. An ant sting injects methanoic acid into the skin. What natural remedy can be used to neutralize it? SCIENCE
• Vinegar
• Lemon juice
• Rubbing with baking soda paste
• Water
Answer: Rubbing with baking soda paste
Methanoic acid from an ant sting can be neutralized by applying a mild base like baking soda (sodium hydrogen carbonate) paste. The base reacts with the acid to reduce the pain.
Q43. Why is it dangerous to mix acids with bases directly? SCIENCE
• They produce a large amount of gas
• They produce a large amount of heat (exothermic reaction)
• They change color
• They become neutral
Answer: They produce a large amount of heat (exothermic reaction)
The reaction between an acid and a base is called neutralization. It is a highly exothermic reaction, meaning it releases a significant amount of heat, which can be dangerous.
Q44. A beaker contains a colorless liquid. A drop of it on a turmeric paper turns it reddish-brown. What is the nature of the liquid? SCIENCE
• Acidic
• Basic
• Neutral
• Sour
Answer: Basic
Turmeric paper is a natural indicator. It turns reddish-brown only when it comes in contact with a basic substance. Therefore, the liquid in the beaker is basic.
Q45. Which base is commonly known as ‘caustic soda’ and has the chemical formula NaOH? SCIENCE
• Potassium hydroxide
• Calcium hydroxide
• Magnesium hydroxide
• Sodium hydroxide
Answer: Sodium hydroxide
The common name for sodium hydroxide (NaOH) is caustic soda. It is called ‘caustic’ because it is a very strong base that can cause severe burns.
Q46. Which acid is known as the ‘King of Chemicals’ and is used in car batteries? SCIENCE
• Hydrochloric acid
• Nitric acid
• Sulphuric acid
• Phosphoric acid
Answer: Sulphuric acid
Sulphuric acid (H₂SO₄) is called the ‘King of Chemicals’ due to its immense industrial importance. A highly concentrated form of this acid is also used as the electrolyte in lead-acid car batteries.
Q47. What is the chemical name and formula for the base found in ‘Milk of Magnesia’? SCIENCE
• Sodium hydroxide, NaOH
• Calcium hydroxide, Ca(OH)₂
• Magnesium hydroxide, Mg(OH)₂
• Ammonium hydroxide, NH₄OH
Answer: Magnesium hydroxide, Mg(OH)₂
Milk of Magnesia is a common name for a suspension of magnesium hydroxide, Mg(OH)₂, in water. It is used as an antacid to neutralize stomach acid.
Q48. Which base is used in the process of whitewashing walls and its solution is known as limewater? SCIENCE
• Sodium hydroxide
• Potassium hydroxide
• Calcium hydroxide
• Ammonium hydroxide
Answer: Calcium hydroxide
Calcium hydroxide, Ca(OH)₂, is the base used for whitewashing. A solution of this compound is called limewater, which turns milky when carbon dioxide is passed through it.
Q49. Acids react with metals to produce a gas. Which gas is produced? SCIENCE
• Oxygen
• Nitrogen
• Carbon dioxide
• Hydrogen
Answer: Hydrogen
When an acid reacts with a metal, it typically produces hydrogen gas. You can test for this gas by bringing a burning matchstick near it – the gas will burn with a ‘pop’ sound.
Q50. If a liquid has a pH of 7, what is its nature? SCIENCE
• Strongly acidic
• Strongly basic
• Neutral
• Weakly acidic
Answer: Neutral
The pH scale measures how acidic or basic a substance is. A pH of 7 is exactly in the middle of the scale and indicates that the substance is neutral, like pure water.