What are the answers to Activity 4, concerning element symbols, periods, groups, and classifications?

Here are the answers to Activity 4:

1. The symbol for sodium is:

   $$\boxed{\text{Na}}$$

2. An element in the same period as helium is:

   $$\boxed{\text{Hydrogen}}$$

3. Two semimetals in the same group as carbon are:

   $$\boxed{\text{Silicon and Germanium}}$$

4. A semimetal and a non-metal in the same period as potassium are:

   $$\boxed{\text{Semimetal: Ge, Non-metal: Br}}$$

5. Classification of elements:

   • a) oxygen: Non-metal
   • b) copper: Metal
   • c) silicon: Semimetal
   • d) phosphorous: Non-metal
   • e) calcium: Metal
   • f) helium: Non-metal