What is the mass of a substance

Which statement accurately describes the relationship between air pressure, air density, or altitude? as altitude increases, pressure increases.as altitude increases, air density increases.air pressure and density are lowest at sea level.denser air exerts more pressure than less dense air.

Consider the nuclear equation below. 239 > x + 4 he 94 2 what is x? 1.235 cm 96 2.243 u 92 3.235 u 92 4.243 cm 96

21. consider the following chemical reaction: n2+ o2 2 no if 10.0 g of n2 reacts with excess oxygen then how many grams of no can be formed? a) 10.7 g b) 21.4 g c) 32.9 g d) 42.8 g page 4 of 8