Chemistry Basics: Elements, Acids & Everyday Reactions: questions and answers
Study every question with its correct answer and explanation.
1. Which metal is a liquid at normal room temperature?
- A. Mercury
- B. Lead
- C. Tin
- D. Zinc
Answer: Mercury
Mercury is the only metal that is liquid at normal room temperature; its symbol Hg comes from 'hydrargyrum', meaning 'watery silver'. Bromine is the only non-metal element that is liquid at room temperature.
2. What is the chemical formula of common (table) salt?
- A. KCl
- B. CaCO₃
- C. NaCl
- D. Na₂CO₃
Answer: NaCl
Common salt is sodium chloride, NaCl, made of sodium and chlorine in a 1:1 ratio. Don't confuse it with washing soda, which is sodium carbonate (Na₂CO₃·10H₂O), or with limestone and marble, which are calcium carbonate (CaCO₃).
3. Which acid gives lemons their sour taste?
- A. Acetic acid
- B. Citric acid
- C. Lactic acid
- D. Oxalic acid
Answer: Citric acid
Lemons and other citrus fruits are rich in citric acid. Vinegar contains acetic acid, sour curd (yoghurt) contains lactic acid, and tamarind is a well-known source of tartaric acid.
4. Which acid is produced in the human stomach to help digest food?
- A. Sulphuric acid
- B. Nitric acid
- C. Hydrochloric acid
- D. Acetic acid
Answer: Hydrochloric acid
Glands in the stomach lining secrete hydrochloric acid (HCl), which kills many germs in food and activates pepsin, the enzyme that begins breaking down proteins. Antacids are mild bases, such as magnesium hydroxide, that neutralise excess acid.
- Advertisement
5. Blue litmus paper turns red when dipped in which of these?
- A. Soap solution
- B. Lime water
- C. Pure water
- D. Lemon juice
Answer: Lemon juice
Acids turn blue litmus red, and lemon juice is acidic. Bases such as soap solution and lime water (a solution of calcium hydroxide) do the opposite, turning red litmus blue, while pure water changes neither.
6. Which gas is commonly called 'laughing gas'?
- A. Nitrogen dioxide (NO₂)
- B. Nitrous oxide (N₂O)
- C. Carbon monoxide (CO)
- D. Ammonia (NH₃)
Answer: Nitrous oxide (N₂O)
Nitrous oxide (N₂O) is called laughing gas because breathing it in can cause a feeling of euphoria; it has long been used as a mild anaesthetic, especially in dentistry. Carbon monoxide, by contrast, is a colourless, odourless and highly poisonous gas.
7. Which two things must be present for iron to rust?
- A. Oxygen only
- B. Water only
- C. Oxygen and water
- D. Carbon dioxide and nitrogen
Answer: Oxygen and water
Rusting is a slow chemical reaction in which iron combines with oxygen in the presence of water or moisture, forming reddish-brown hydrated iron(III) oxide — rust. Coating iron with a layer of zinc, called galvanisation, is a common way to prevent it.
8. Which gas is dissolved under pressure in soft drinks to make them fizzy?
- A. Oxygen
- B. Nitrogen
- C. Hydrogen
- D. Carbon dioxide
Answer: Carbon dioxide
Carbon dioxide is forced into the drink under pressure; when you open the bottle, the pressure drops and the gas escapes as bubbles. Dissolved CO₂ also forms weak carbonic acid, which gives fizzy drinks their slightly sharp taste.
9. Which is the most abundant element in the Earth's crust by mass?
- A. Oxygen
- B. Silicon
- C. Aluminium
- D. Iron
Answer: Oxygen
Oxygen makes up nearly half of the Earth's crust by mass, mostly locked in rocks and minerals as oxides and silicates. Silicon comes second, and aluminium is the most abundant metal in the crust.
10. Which noble gas gives the classic glowing advertising signs their reddish-orange light?
- A. Helium
- B. Neon
- C. Argon
- D. Xenon
Answer: Neon
When electricity passes through neon gas in a sealed tube, it glows a bright reddish-orange, which is why such lights are called 'neon signs'. Noble gases have a full outer electron shell, so they are very unreactive; argon is used to fill ordinary incandescent light bulbs.