3.) A certain tank contains a mixture of nitrogen, oxygen, and helium gases. The partial pressure of nitrogen gas is 503 mmHg. The partial pressure of oxygen gas is 481 mmHg. If the total pressure of the gas mixture is equal to 1291 mmHg.
What is the partial pressure of the helium gas?

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom. 

Following are the  advantages of the parametric equations: 1) they can be used to graph curves that are not functions, like the unit circle.2) the parameter can be used to represent the quantity that is  useful to  provide us with better information about the graph.3)  it is useful to convert between rectangular equations and parametric equations.with specific reference to chemistry,  parametric equations are employ for solving hydrogen and hydrogen-like ions, quantum mechanically. herein, cartesian coordinates are converted in spherical polar coordinates. the solution obtained, when plotted on spherical polar graph paper, provides visualization of atomic orbital such as s,p,d and f.