Answer:
The answer is B an open system allows energy and mass to move in and out of it
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25 people in an elevator that has a maximum load of 20 people
You should be checking your gas appliances every year, it should always be a qualified technician.
Phosphorus is in group 15 meaning it have 5 valence electrons. This means that it needs 3 more electrons to create a full outer shell. As these three electrons are negatively charged it means that P is a 3- ion (it’s an anion [negatively charged ion])
