Astatine. Because it has the smaller shell of electrons. I believe
Density = (mass) / (volume)
Density = (17.0 g) / (25.3 cm³) = 0.672 gm per cm³. (rounded)
Answer: Total pressure inside of a vessel is 0.908 atm
Explanation:
According to Dalton's law, the total pressure is the sum of individual partial pressures. exerted by each gas alone.
= partial pressure of nitrogen = 0.256 atm
= partial pressure of helium = 203 mm Hg = 0.267 atm (760mmHg=1atm)
= partial pressure of hydrogen =39.0 kPa = 0.385 atm (1kPa=0.00987 atm)
Thus 
=0.256atm+0.267atm+0.385atm =0.908atm
Thus total pressure (in atm) inside of a vessel is 0.908
The answer is C. Elastic potential energy
Chemistry is concerned with:
1) Composition
The composition of matter helps determine how it will behave chemically and physically, and is studied in chemistry
2) Structure
The structure of a certain element or compound also governs how the substance behaves, making it another vital aspect of chemistry
3) Behavior
The behavior of substances is studied in order to have explanations presented for it, expanding our understanding.
