The answer should be the third option "number of protons and neutrons." The atomic mass of a element is equal to the amount of protons, and neutrons added together in that element. So for example if we are trying to find the atomic mass of hydrogen you would add the total amount of protons and neutrons together to find it's mass although it doesn't equal the exact amount of it's mass but it's close.
Hope this helps.
Osmosis is 98% water and 2% salt inside the cell.
Answer:
2.1 located between the left atrium and the left ventricle (left atrioventricular orifice).
2.2 it helps to prevent blood from flowing backward as it moves through the heart.
