 I have some water and some alum crystals with me. Now what I'll do is I will crush these crystals with the help of this hammer like this and then add the powdered alum into this water over here. Now I will mix the alum with the water. I will try and dissolve it. So we see all the alum has been dissolved. And now what we'll do is we will crush some more alum crystals and then again add the powdered alum into this water. Now again we will try and dissolve it. So what we see is after adding the powdered alum the second time not all of the alum has been dissolved. Some of it is settled at the base of this glass jar. So now we will heat this mixture and after heating we will try and dissolve the powdered alum again. And now we see that all of the alum has been dissolved. So what we will do now is we will add some more alum into this mixture. And then again try and dissolve it. Now what we'll do is we will take one alum crystal, tie it with a string and tie the other end of the string with the pen that you see over here. And then hang the crystal into the water like this. Make sure the crystal does not touch the base of the glass jar. We will keep it like this for at least four to five days. And now after four to five days let's see what happens. Look at the size of the crystal. Has it grown bigger? The size of the crystal has increased. So the question now is is this a physical change or a chemical change? Think about it. Well turns out this is a physical change. We started from alum crystals and then again finally we did get back all of those alum in the form of crystals. The crystal that we hung it grew bigger. Look at the size difference in front of you. We did crush the crystals to begin with but then we were able to obtain those crystals back from the water. So we started with alum crystals and we ended with alum crystals. There was no new substance that was formed and this process as we saw is also reversible. So turns out this is a physical change. Now let's look at one more example. How about when you plant seeds in a soil? After some time in fact after months you see plants growing from those seeds, right? What kind of a change is this? Is this physical change or a chemical change? Well turns out this is a chemical change because you can see new substances being formed. Just from seeds you're able to get a whole plant. New substances are formed. New materials are formed. You can see leaves forming, stems forming. All of these new substances are forming and just from seed. And also once you have the plant you cannot go back and get the seed from where it came from. So turns out growing of plant from seeds is a chemical change.