It is the mass of one mole of the substance.
Proton plus neutron is the correct answer. Protons and neutrons have a mass of 1 and electrons have a mass of 0. So in order to find the mass of an atom you need to add the number of protons and the number of neutrons.
EVAPORATION OR THE ANIMALS ARE DRINKING THE WATER BECAUSE IT IS HOT
There are 5 steps:
1- measure the mass of the container
2- measure the volume of the liquid
3- measure the combined mass of the liquid and the container.
4-determine the mass of the liquid alone
5-divide the mass by the volume.
Answer: We do not know. We have not been given the solubility of oxygen in water at a given temperature nor have we been given the Henry's laws constant. We also do not know whether you mean 1 atmosphere of air, or 1 atmosphere of oxygen.