At ground level gases outside and helium inside are in static equilibrium with balloon as separating surface. Both balloon and atmospheric forces are compressing to maintain that state.
But as balloon moves upward because of less density of helium gas in balloon internal force of helium gas increases. At high altitude atmospheric pressure decreases due to gravitational pull and fluid nature of gas. So equilibrium reestablish and it start to expand at high altitude.
Electron affinity increases upward for the groups and from left to right across periods of a periodic table because the electrons added to energy levels become closer to the nucleus, thus a stronger attraction between the nucleus and its electrons.
Nitrate is a polyatomic ion with the molecular formula NO⁻₃ and a molecular mass of 62.0049 u. Organic compounds that contain the nitrate ester as a functional group are also called nitrates.
