Suppose three neutrons are released when an atom in a sample of fissionable nuclei undergoes fission. Each of these neutrons has enough energy to cause another fission reaction in another nucleus of the material. If the reaction is not controlled, how many atoms will have undergone fission after 2 more stages of the chain reaction?

13 nuclei

Explanation:

From the question, the fission of one nucleus produces three neutrons which causes  more nuclei to undergo fission.

This implies that, after the first fission, three neutrons cause three nuclei to undergo fission. The three nuclei that underwent fission produces nine neutrons which causes the fission of nine nuclei.

All together we the number of nuclei that underwent fission as;

1 + 3 + 9 = 13 nuclei.

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

no, the red giant is the hottest with 2.00.000.000 degrees celsius. while the white dwarf only 25,000 degrees celsius.