They become more stable because they achieve a full outer shell of valence electrons with the magic number of 8.
When all the electrons are placed in their orbitals!!!
Burrows, tracks, coprolites, nests and footprints are examples of traces that can be found in a fossil.
We should describe a little bit the legend.
A - Element - we should have circles with same color and not bonded together (argon gas).
B - Compound - here we may have circles with same or different color bonded together (water or oxygen which is a diatomic molecule).
C - Mixture of elements - circles with different colors not not bonded together (mixture of noble gases).
D - Mixture of compounds - circles with same or different color bonded together but we should see two or more types of connectivity between circles (mixture of water and ethanol).
E - Mixture of elements and compounds - circles with same or different color bonded together mixed with circles with same color and not bonded together (a mixture between oxygen which is a diatomic molecule and noble gas like argon).
Now we may answer the question:
1) B
2) C
3) D
4) D
5) A
6) B
7) B
8) E
9) E
10) D
11) B
12) D
13) D
14) D
15) D
