How close a measured value is to the value is to the accepted value

If a gas has an initial pressure of 101kpa and a volume of 10l, then it expands to a volume of 20l, what is the new pressure?

What are the coefficients to balance the following equation? ba+br=babr2

Acertain atom has 22 protons and 19 electrons. this atom loses an electron. the net charge on the atom is now 4+1+01-4-. if this same atom with 22 protons and 19 electrons were to gain 3 electrons, the net charge on the atom would be 3+2+02-3-.