A sample of gas has a volume of 215 cm3 at 23.5 °C and 3 atm. What will the volume of the gas be at STP

1) how many electrons are in each energy level of the following elements? a. he b. na c. na d. ne 2) how many valence electrons are percent in the following atoms? a. s b. mg c. be d. cl 3) which of the following elements are stable as atoms? a. he b. o c. cl d. ar if you are able to provide the work as to how you got the answers that would be greatly appreciated. : )

Iknow the answer is a but i don't know why

Drag each label to the correct location on the chart. classify each reaction as endothermic or exothermic.