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Here is the link to a great video that explains your question nicely, hope this helps.
Answer:
6
Explanation:
This atom is sulfur (if the electrons are equal to the protons/not an ion). You can tell the number of valence electrons by looking at the individual shell. The first shell (1s) can only hold 2 electrons. The second shell (2s and 2p) can hold 8 electrons. The third shell (3s and 3p), which is the valence shell, only has 6 out of its possible 8 electrons, so this atom has 6 valence electrons.
Answer:
8.33 moles CO2 X. 25mol O2. 16mol CO2. = 13.0 moles
I think maybe reptiles bu i could be wrong. :)