1.50 mol ne, 2.65 mol ar, and 1.75 mol xe. what is the partial pressure of xe?

Mole fraction of Xe = moles of Xe/Total moles
                               = 1.75/1.75 + 1.50 + 2.65
                               = 1.75/5.9
                               =    0.29.

∴Partial pressure of Xe = Total pressure x mole fraction of Xe
                                      = Total pressure x 0.29
 
Total pressure will be given to you. 

The total number of nucleons