Which of the above symbols represents a switch?

Here are the solutions to the questions:

4. After 30 minutes the wooden spoon did not get hot. This was because it...

   • Wood is a poor conductor of heat, meaning it does not transfer heat easily. This property is why wooden spoons are used for cooking. The correct option is B.
   $$\boxed{\text{B}}$$

5. The cheapest way of water treatment is...

   • Boiling requires fuel/energy, which can be costly. Chlorination requires chemicals. Filtration can range from very simple (e.g., using a cloth or sand) to complex, but basic filtration methods are often the cheapest for removing suspended particles. Salting is not a method for making water potable. Among the given options, simple filtration is generally the most inexpensive method for initial water treatment. The correct option is C.
   $$\boxed{\text{C}}$$

6. Study the diagrams showing different symbols of electricity below. Which of the above symbols represents a switch?

   • Symbol 1 represents a cell or battery.
   • Symbol 2 represents a resistor.
   • Symbol 3 represents a lamp or bulb.
   • Symbol 4 represents an open switch. The correct option is D.
   $$\boxed{\text{D}}$$

7. People wash their bodies regularly in order to...

   • Regular washing helps remove dirt, sweat, and microorganisms (germs and bacteria) from the skin, which prevents body odor and reduces the risk of infections. The correct option is A.
   $$\boxed{\text{A}}$$