12. molecules of hydrogen escape from earth, but molecules of oxygen and nitrogen are held to the surface. why?

            Because Hydrogen gas is lighter than Oxygen and Nitrogen Gases.

                        Those molecules will escape from earth which can overcome the earth's gravitational pull. Therefore, molecules small in size, lighter in weight and with high velocity can escape from earth's surface.

The masses of given molecules are as follow,

                      M.Mass of Hydrogen  =  H₂  =  2.02 g.mol⁻¹

                      M.Mass of Nitrogen  =  N₂  =  28.02 g.mol⁻¹

                      M.Mass of Oxygen  =  O₂  =  32.00 g.mol⁻¹

Hence, Hydrogen has far less molecular mass than oOxygen and Nitrogen gases. Also, according to Graham's law of Effusion, Hydeogen will move faster than the remaining two.

he uptake of drugs from the intestine is often strongly influenced by diffusion. for example, consider a water-insoluble steroid for treating inflammation that is solubilized in aggregates of detergent molecules, called micelles. these micelles, aggregates of 80 soap molecules, have a molecular weight of 24,000, a diameter of 2.6 nm, and a charge of -27. the positively charge ions (counterions) in this system are na".

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.