- Q: What is an element?
A: An element is a pure substance made of only one kind of atom.
- Q: Give two examples of elements.
A: Oxygen and gold.
- Q: How many naturally occurring elements are there?
A: Around 92.
- Q: Who is called the father of the periodic table?
A: Dmitri Mendeleev.
- Q: What is the smallest unit of an element?
A: An atom.
- Q: Which element do we breathe in for survival?
A: Oxygen.
- Q: Which element makes up most of the Sun?
A: Hydrogen.
- Q: What element is used in thermometers?
A: Mercury.
- Q: Which element is called a noble metal?
A: Gold.
- Q: Which element is essential for our bones and teeth?
A: Calcium.
- Q: Are all elements metals?
A: No, some are metals, some are non-metals, and some are metalloids.
- Q: Name one property of metals.
A: They are good conductors of electricity.
- Q: Name one property of non-metals.
A: They are usually poor conductors of heat.
- Q: Is carbon a metal or non-metal?
A: Non-metal.
- Q: Which element is liquid at room temperature besides mercury?
A: Bromine.
- Q: What element gives a reddish color to our blood?
A: Iron.
- Q: Which element is found in diamonds?
A: Carbon.
- Q: What is the symbol of sodium?
A: Na.
- Q: What is the symbol of potassium?
A: K.
- Q: Name one element that does not react easily with other elements.
A: Helium.
- Q: What is a compound?
A: A compound is a substance made of two or more elements chemically combined.
- Q: Give one example of a compound.
A: Water (H₂O).
- Q: What elements make up water?
A: Hydrogen and oxygen.
- Q: What elements make up carbon dioxide?
A: Carbon and oxygen.
- Q: Is salt (NaCl) an element or a compound?
A: A compound.
- Q: Can compounds be broken into simpler substances?
A: Yes, by chemical methods.
- Q: What is the chemical name of chalk?
A: Calcium carbonate (CaCO₃).
- Q: Is sugar a compound?
A: Yes, it is made of carbon, hydrogen, and oxygen.
- Q: Which gas is formed when hydrogen burns in oxygen?
A: Water vapour.
- Q: What happens to the properties of elements when they form a compound?
A: They change completely.
- Q: Is water tasteless or does it have the taste of hydrogen and oxygen?
A: It is tasteless; compounds have new properties.
- Q: Can we separate the elements of a compound by physical methods?
A: No, only by chemical methods.
- Q: Is rust a compound?
A: Yes, it is iron oxide.
- Q: Is carbon dioxide useful for plants?
A: Yes, plants use it for photosynthesis.
- Q: Why is carbon monoxide harmful?
A: Because it prevents blood from carrying oxygen.
- Q: What is the chemical formula of ammonia?
A: NH₃.
- Q: What is formed when iron and sulphur are heated together?
A: Iron sulphide (a compound).
- Q: Is oxygen in water free or chemically combined?
A: Chemically combined.
- Q: Does sodium chloride taste like sodium or chlorine?
A: No, it has a completely new taste (salty).
- Q: Which compound is called quicklime?
A: Calcium oxide (CaO).
- Q: What is a mixture?
A: A mixture is formed when two or more substances are combined physically.
- Q: Give one example of a mixture.
A: Salt in water.
- Q: What is air made of?
A: A mixture of gases like nitrogen, oxygen, carbon dioxide, etc.
- Q: Is sand and sugar a mixture?
A: Yes, if mixed physically.
- Q: Can mixtures be separated easily?
A: Yes, by physical methods.
- Q: What is the difference between a mixture and a compound?
A: Mixtures are physical, compounds are chemical.
- Q: Is milk a mixture?
A: Yes, it is a colloid.
- Q: Is sea water a mixture or compound?
A: A mixture (salt + water + minerals).
- Q: Can we see the particles in all mixtures?
A: No, in some mixtures (like solutions) they are invisible.
- Q: What is a solution?
A: A uniform mixture where one substance dissolves in another.
- Q: How can you separate sand and iron filings?
A: By using a magnet.
- Q: How can you separate salt from water?
A: By evaporation.
- Q: How can you separate husk from rice?
A: By winnowing.
- Q: How can you separate oil from water?
A: By decantation or using a separating funnel.
- Q: How can you separate cream from milk?
A: By centrifugation.
- Q: How can you separate muddy water?
A: By filtration.
- Q: How can you obtain pure water from seawater?
A: By distillation.
- Q: How can you separate a mixture of colours in ink?
A: By chromatography.
- Q: What method is used to separate heavier solids from liquids?
A: Sedimentation.
- Q: How can farmers separate stones from grains?
A: By handpicking.
- Q: Is bronze an element, compound, or mixture?
A: A mixture (alloy of copper and tin).
- Q: Is steel a compound or mixture?
A: A mixture (alloy of iron and carbon).
- Q: Why is air called a mixture and not a compound?
A: Because gases are not chemically combined.
- Q: Why can we smell perfume across the room?
A: Because perfumes are mixtures that diffuse easily.
- Q: Why is lemonade a mixture?
A: Because lemon juice, sugar, and water are physically mixed.
- Q: Is soil a mixture?
A: Yes, it contains sand, clay, humus, and minerals.
- Q: Why do we use alloys instead of pure metals?
A: Because alloys are stronger and more useful.
- Q: Is diamond a mixture?
A: No, it is pure carbon, so it is an element.
- Q: Is rusting a physical or chemical change?
A: A chemical change.
- Q: Why is it important to know the difference between mixtures and compounds?
A: Because it helps in separating, using, and understanding substances in daily life.