I have these 4 glasses and a small beaker with some water in it. I have vegetable cooking oil and a plate with some salt, sugar, halvi, that is turmeric and some flour. I will add some amount of these substances in these glasses. Stir it, try to mix it and I want you to see, I want you to observe what happens. Ok so let's do it. I will start with salt. Next comes sugar. Then it's turmeric or halvi and finally some flour. Ok now I will try and stir it. Ok now let's look at each of these glasses closely. So we start with salt and what do we observe? We observe that salt has disappeared completely in water right. Let's look at the glass with sugar. Again here we see that most of the sugar has disappeared completely. There is some left and if you keep on stirring it, even that will disappear completely in water. Let's look at the third glass now. Well over here if you look closely, we see halvi sort of settling at the bottom of the glass right. If you look at the top, you have a look at this. Some of the water appears clear at the top. And we see halvi sort of settling down right. Let's look at the fourth and the final glass. And similarly here we see some of the flour settling at the bottom of the glass. If you look at it from the top, we see this water is somewhat clear and all the flour is settling at the bottom. It's not disappeared completely. So it turns out some substances disappear completely in water while some don't. And the substances which disappear completely after mixing it a little, those substances are called soluble substances and the ones that do not disappear completely. Those are called insoluble substances. So these were just some of the examples of soluble and insoluble substances. There are many more. This is one way of categorizing substances. We can categorize substances based on their solubility and water. Some substances are soluble, some aren't. And the same goes for liquids as well right, we dissolve solids. Let's try and dissolve this vegetable cooking oil into this beaker of water. Okay, so I've added some oil. Now let's try and dissolve it. Well, it turns out that oil is actually not disappearing right. It's rather settling at the top of the beaker. Look at this. So it turns out oil and in fact all sorts of oil, I took vegetable cooking oil. Even if we take coconut oil or carocene, no oil is disappearing when I try to mix it with water. So that means these liquids are insoluble in water. So we talked about the solubility of some solids. We talked about the solubility of some liquids. We can also talk about solubility of gases. Some gases are soluble in water while some are it. For instance, an example of a gas that is soluble in water is oxygen. Water usually has small quantities of oxygen dissolved to it. And it is very important for the survival of animals and plants that live in water. So from this activity, we saw that we can categorize, we can group some substances based on their solubility in water. The ones that disappear when you try to mix it with water, those are called soluble substances. And the ones that do not disappear upon mixing are called insoluble substances.