How many moles are in 68.5 liters of oxygen gas at stp?

Asample of radium-226 will decay 1/4 of its original amount after 3200years. what is the half-life of radium-226?

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

How hot is the suns corona? (integrated science)