Alright guys, so where we left off, which of the following compounds would be optically active. So remember Kyrill compounds are optically active. So for something to be optically active, it has to have a carbon connected to four different groups. It needs a Cairo carbon. So remember every end, every corner is a carbon. So here go a bunch of carbons. So all these are carbons. So if we take a look at the first one, carbon is tetra valent, must make four bonds. So this one here is making three bonds to get to four, can't be carol, it's not connected to four different things. This one is connected to two HS. Can't be Carl and this one is connected to two ages, can't be carl to be a Cairo carbon. Every of every single one of the four groups connected to, you have to be different from each other here. This would be a CH three, CH two. Here, this is a ch so this has potential CH two is out & CH three is out now that middle carbon has potential, it is connected to an H A C. L. But then it's connected to two Ch two. Ch 3s. They're both exactly the same. So this is not carol. And then here there's three carbons on this three hydrogen on this one, one on this one. So that has a potential one on this one that has potential three on this one, That's AC H three. And this is a CH three. So obviously the ones that are CH three are out, they're not connected to four different things, Look at this carbon here, it is connected to an H. In O. H. A. C. H. Three. And then this big group that is not a CH three. So that is a Cairo center right there. So this is gonna be optically active. This carbon here is connected to an H. But then it's connected to two CH 3s. It is not Cairo, but it's okay because we found out that this one here is karl. So that's our answer. If we look at the last option, why is it not carol? Well here this is connected to three H. S. Because it needs to get to four bonds. This one's connected to one, This one here is connected to three, So the ones connected to three hydrogen scampi Carl. And then this carbon here is not carol either because it's connected to two CH three's. Two of the same things can't be Cairo. So remember, a Cairo compound is optically active. It can bend light either to the left or to the right. That's the fundamental idea you need to take from this section