Available Answers

1. 1.

   Fill in the blanks.

   1. ______________ is anything that has mass and occupies space.
   2. A pure substance can be an _____________ or a _____________.
   3. The particle theory of matter states that matter is made up of _________________.
   4. _________________ is the force of attraction that exists between the particles in matter.
   5. The particles of _________________ do not change their position but vibrate to and fro at their mean positions.
   6. A __________________ change is the change that we want to take place and is useful to us.
   7. Heat is ___________________ in an endothermic change.
   8. A chemical change is _________________ and _________________.
   9. The rate of evaporation __________________ with the increase in temperature.
   10. __________________ is the process by which a liquid transforms into semisolid mass.
   11. __________________ possess properties of both metals and non-metals.
   12. An _________________ is the smallest particle of an element that takes part in a chemical reaction.
   13. The molecules consisting of one atom of an element are called __________________ molecules.
   14. The homogenous mixture of a solvent and solute is called the ___________________.
   15. A substance is said to be __________________ if it passes from the solid state directly into the gaseous state without changing into a liquid.
   16. In order to form a ___________________, atoms always combine in whole numbers.
   17. __________________ is defined as the combining capacity of an element.
   18. A positively charged ion is called a ____________________.
   19. A group of atoms of different elements functioning together as a single unit and carrying a charge is known as a ____________________.
   20. Elements which possess valency 1 are called ____________________.
   21. The substances that combine or react are known as ____________________.
   22. A __________________ is a substance that changes the rate of a chemical reaction without itself undergoing any chemical change.
   23. Combination reactions are also called _________________ reactions.
   24. The valency of noble gases is ___________________.
   25. A __________________ represents the number of atoms of each element present in a molecule or the compound.
   26. ___________________ is a brittle metal.
   27. The more ___________________ a metal, the more readily it corrodes.
   28. ____________________ is the purest form of iron and contains less than 0.1 per cent of carbon.
   29. ____________________ is used as propellant for spacecraft.
   30. Metalloids such as ___________________ and ___________________ act as semiconductors.
   31. Air is matter and therefore it occupies ___________________ and has ____________________.
   32. The blanket of air that surrounds the earth is called _____________________.
   33. The lowest temperature at which a substance must be heated before it begins to burn is called its ______________________.
   34. The circulation of oxygen in nature is known as ____________________.
   35. Carbon dioxide dissolves in water to form a weak acid called ______________________.
2. 2.

   State whether the given statements are true (T) or false (F).

   1. All things around us occupy space that make them similar to each other.
   2. The particles of matter move around in the space occupied by them.
   3. The molecules are tightly packed in liquids.
   4. An element consists of very small particles called atoms.
   5. Water is a compound which consists of hydrogen and oxygen elements combined together in a fixed ratio of 3:1.
   6. Ripening of fruits is an undesirable change.
   7. A physical change is temporary and can be reversed by changing the conditions in most cases.
   8. Photosynthesis helps us to release energy needed by the cells of the body.
   9. Evaporation is a surface phenomenon.
   10. Burning is a chemical change that can be reversed.
   11. Both elements and compounds have fixed composition and a definite set of properties.
   12. Metals like potassium, calcium and sodium have low melting and boiling points.
   13. Sulphur is a triatomic molecule.
   14. A formula indicates the elements present in a compound.
   15. Energy is released or absorbed during the formation of a mixture.
   16. An atom of an element shows all the properties of that element.
   17. Molecules are of three types: molecule of an atom, molecule of an element and molecule of a compound.
   18. When electric current is passed through acidulated water, it decomposes to give hydrogen and oxygen gases.
   19. Oxygen and nitrogen are polyatomic molecules.
   20. An ion is a charged particle that carries a positive or negative charge.
   21. The atoms of the molecules of the reactants rearrange themselves to form one or more products.
   22. Respiration is a photochemical reaction.
   23. Carbon dioxide combines with water to form carbonic acid.
   24. The products are always written on the left-hand side in a chemical equation with a plus sign between them.
   25. The chemical formula of copper sulphate is Ca₂SO₂.
   26. Copper and silver occur in both free and combined states.
   27. Lead and arsenic are good conductors of heat and electricity.
   28. Both air and water are necessary for rusting of iron to take place.
   29. Lead is a silvery metal which is liquid at room temperature.
   30. Antimony is used in storage batteries.
   31. The composition of air is not constant everywhere.
   32. Non-metals burn in oxygen to produce their respective oxides which are basic in nature.
   33. A mixture of oxygen and nitrous oxide is used as a medical anaesthesia gas.
   34. Nitrogen is reactive and reacts with most elements.
   35. Carbon dioxide is neither combustible nor a supporter of combustion.
3. 3.

   Why is it important to understand matter?
4. 4.

   Why are solids rigid and hard ?
5. 5.

   Why do liquids have low density?
6. 6.

   Why are the gases highly compressible?