Answer:
Let x moles of silicon contains 2.8x10^24 atoms. 6.02x10^23 atoms are present in 1 mole of Si. Therefore 2.80x10^24 atoms are present in = 2.8x10^24/6.02x10^23 = 4.65 moles of Si.
Explanation:
Chromatography separates things according to their weight.
B.
The cynobacteria were already there without the oxygen, so that rules out A, and a lot of prokaryotes were anaerobic, so that rules out C. Finally, Photosynthesis does not require oxygen. Instead, Oxygen is a waste product of it. Therefore, it cannot be D. So, we are only left with B
Hoped this helped :D