Helppp Energy and Matter Electric power plants that use nuclear fission reactions rely on a controlled self-sustaining chain reaction
of splitting atoms. By examining the diagram for nuclear fission,
explain how a chain reaction might occur. Explain why it is
important to control the rate of the chain reaction.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

the answer is na (sodium)