2 also called pulmonary surfactant. one of certain lipoproteins that reduce the surface tension of pulmonary fluids, allowing the exchange of gases in the alveoli of the lungs and contributing to the elasticity of pulmonary tissue.
Helium is commercially recovered from natural gas deposits, mostly from Texas, Oklahoma and Kansas. Helium gas is used to inflate blimps, scientific balloons and party balloons. It is used as an inert shield for arc welding, to pressurize the fuel tanks of liquid fueled rockets and in supersonic windtunnels.
3) That's right. Some, maybe all, of the liquid will evaporate into gas, filling the empty space. Now if all the liquid evaporates, we just have a box of gas. That's not what we want. So let's suppose that only some of the liquid evaporated and that there are both the liquid state and the gas state present in the box. The gas that is above the liquid is called its vapor and it creates a pressure called vapor pressure. What I mean is this: suppose you put a gas-pressure measuring device into the gas and never touched the liquid.