To make 300 ml of oxygen at 20 degrees change it’s volume to 250 ml, what must be done to the sample if it’s pressure and mass are to be held constant ?

Hope the image of the frequency formula

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. 

The answer is d.potassium

The molar mass of a substance is defined as the mass of 1 mol of that substance, expressed in grams per mole, and is equal to the mass of 6.022 × 10 23 atoms, molecules, or formula units of that substance.