 Now, please find out that according to kinetic theory of solids before the break, how many flexible bonds on what molecule has. Only 2 hydrogen bonds, 3 hydrogen bonds, this is also 6, the vibration can happen along direction. It will not leave everything else and start moving independently. So, translation as rotational, 0, close to 0, only vibrational, okay, because it is held by the hydrogen bonds from 3 sides. So, total 88, how much it is, joule per mole per kg. Now, tell me at 15 around, joule per gram, 4.18. So, you can apply the kinetic theory on solids as a layer on liquid and you will get, so it is a very strong. Now, can you tell me, I miss one small portion at the start. So, can you find out the root wing square velocity in terms of temperature, right? As a function of monotomic, this is equal to 1, this can be written as number of u square is equal to 3 by 2 rt and then root, which is the log state and also the velocity. This I think you might have, you are asking as if you, look over here, try it out, free path, main free path is the average distance between the two collisions, main free path is the average distance between the two collisions and why are you finding it, because it is very close to the level. Other reason, if suppose collision happens, suppose a molecule comes and collides with less, mean free path less means without going straight line, straight line way, it diffuses because, so if you have higher mean free path, okay, all these things will be useful when you do engineering, you will learn more about it why it is so useful, but I am just telling you the correct software thing. So, that is how you are finding a mean free path, all right. Now, its motion will go straight, so because there is, so between will not collide with this atom, but it will collide and it will just touch this atom and it touch that atom. So, basically the center of the neighboring atoms should be inside this cylinder for this atom and will collide anything that is coming inside the cylinder, is that clear, okay. So, how many collisions will happen, so if this is the volume, so that many and this many collisions, find these were collisions, this is number of collisions, time between two collisions, suppose these are five collisions, five collisions in one second, so one collision in, so one divided by two collision, now tell me distance between the two collisions, so yes, so the mean free path should be equal to velocity into that, right, which will be one divided by two, so whenever some stupid thing that we have done, so tell me what you have done. So, what is that? Keep on going in a straight line, no, not being like enough attention, okay. So, what happened? Very collision doesn't change the direction, because these are not just assumptions, they are stupid assumptions, okay. So, actually it should be less than one divided by root two times N pi t square, this is the correct expression, we just plot a graph. Let's do one numerical before, you need to find out mean free path for water molecule, the value of number of collisions are important. So, how many water molecules are there in 0.6 kg? Because 0.6 kg is the volume, isn't it? 0.6 kg has number of molecules equal to 600 grams divided by, don't make me do that. So, how many water molecules are there in 0.6 kg? 10, it can be very small, don't tell me the number of particles, how much? 0.028, no. 1 divided by D square, that is 16 into 10 is called minus 20. No one gets close to the answer. So, that's it for this chapter, okay, but the answer given is 4 into 10 is to the power minus 7 meters, the information given in 13.1 is from there only I told you, okay. So, that's it for this chapter.