The answer is B plastic bags made from petroleum.
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Formation of a precipitate
Tc is Technetium, and it has an atomic number of 43. Its atomic configuration is [Kr] 5s(1) 4d(5) [I'm on my phone so I can't do numbers on shoulders, pretend that 1 and 5 are on the s and d's shoulder]
The outside most ring is the 4d(5), and the d orbital can hold ten electrons.
Valence electrons are electrons, in you could say the outside ring that isn't filled, the extra ones. In this case, there are 5.
