What element has 3 valence electrons in the 3rd energy level

The chart shows the bid provided by four contractors to complete a job. which contractor is the most cost-effective?

8) a mixture of he, ne and ar has a pressure of 7.85 atm. if the ne has a mole fraction of 0.47 and 8) ar has a mole fraction of 0.23, what is the pressure of he? a) 4.2 atm b) 3.7 atm c) 5.5 atm d) 2.4 atm e) 1.8 atm

If 22.5 liters of oxygen reacted with excess of hydrogen, how many liters of water vapor could be produced?