 In this video, we will be talking about a new type of reaction called redox reaction. And these are very commonly found. Photosynthesis is an example of redox reaction. The chemical reaction that happen within a battery which powers your phone or laptop devices, this is also an example of redox reaction. In fact, the type of chemical reaction that happen within you to break down sugar and give you energy to run and play is also an example of redox reaction. So let's understand more about these reactions. So in short, any reaction in which both reduction and oxidation happens at the same time, that will be called as redox reaction and that's how it gets its name of redox. So both reduction and oxidation should be happening. And in a separate video, we have talked about this in much detail about oxidation and about reduction. So over here, I will quickly summarize them. So in oxidation, oxygen gets added to a substance. Oxygen addition is called oxidation and I have an example of that. Here in this example, oxygen is getting added to magnesium and we get magnesium oxide. And reduction, it is totally opposite of oxidation. In reduction, oxygen gets removed from a substance. So minus O2 and I have an example of that also. Here in this example, zinc oxide reacts with carbon to give zinc plus carbon monoxide. So you can see that initially, zinc was combined with oxygen, zinc oxide. But over the reaction, it is losing the oxygen. So since oxygen is lost by zinc, zinc is getting reduced. Now this was the definition of oxidation and reduction in terms of oxygen. But we can define oxidation and reduction in terms of hydrogen also. So the definition of oxidation in terms of hydrogen is totally opposite the definition in terms of oxygen. See when oxygen gets added, we call it as oxidation. Whereas when hydrogen gets removed, we call it oxidation minus H2. And I have an example of that. Here methane reacts with oxygen to give carbon dioxide and water. So methane is carbon and a lot of hydrogen. And over the course of this reaction, carbon is losing all of its hydrogen and forming carbon dioxide. So since carbon lost the hydrogen, it's going under oxidation. And reduction will be opposite of this. In reduction, hydrogen will get added. And you can see that this definition in terms of hydrogen is opposite of what the definition is in terms of oxygen. When oxygen is removed, it's called reduction. Whereas when hydrogen is added, it's called reduction. And I have example of this also. Where hydrogen is getting added to sulfur and that's why sulfur is getting reduced. And if you are wondering where is this hydrogen coming from in this definition, then you know we have talked about this in the video of oxidation and reduction. So you should go and watch that first. And if you are confident with this, then let's go ahead and see some examples of redox reaction. So here I have zinc oxide that is reacting with carbon to give me zinc and carbon monoxide. So we focus over here on zinc. So initially zinc was combined with oxygen, zinc oxide. But during the course of reaction, zinc is losing its oxygen. Zinc has lost its oxygen in the reaction. And loss of oxygen, we saw that it is called reduction. We name it as reduction reaction. So zinc is undergoing reduction reaction. But if we focus on the carbon, see finally, carbon is attached with oxygen. But initially, carbon did not have oxygen to begin with. So we can say that over this course of reaction, oxygen gets added to carbon. And addition of oxygen, that is oxidation, we name it as oxidation reaction. And since both reduction and oxidation are happening in the same reaction, we will call this as a redox reaction. Now if you understand this, let's solve some more problems. So for each of these reactions, let's try to find out which element is undergoing oxidation and which is undergoing reduction. And before I solve it for you, why don't you pause and try to yourself first. Now if you have tried it, let's see. So here I have carbon reacting with iron oxide and giving me iron plus carbon dioxide. So if you focus on the carbon, you see initially carbon was alone. But after the reaction, carbon is combined with oxygen. Okay. That means oxygen is getting added to carbon during this reaction. And we know that oxygen's addition is called oxidation. So carbon is going under oxidation reaction. Now let's focus on iron. See iron was combined with oxygen. But during the course of reaction, iron has lost all of its oxygen. So iron is losing its oxygen. And we know that loss of oxygen is reduction reaction. So iron is going under reduction reaction. And since both oxidation and reduction are happening in the same reaction, this is also an example of redox reaction. Now let's look at another one. Here I have NH3. This is called ammonia. And this is reacting with bromine to give me nitrogen plus HBr. Now if we focus on nitrogen, you see initially nitrogen and hydrogen, they were combined. But during the course of reaction, nitrogen has lost its hydrogen. It's losing its hydrogen. Now loss of hydrogen is called oxidation reaction. Okay. Nitrogen is losing its hydrogen. And this is oxidation. Now how I like to remember this is basically loss of hydrogen or minus H2 can also be thought in terms of oxygen as plus O2. These two will have the same effect. And I know that addition of oxygen is oxidation. That's why removal of hydrogen that will also be named as oxidation. So yes, nitrogen is being oxidized here. Now if you focus on bromine, you see bromine to begin with. It wasn't combined with anything. But after the reaction, you see hydrogen is combined with bromine. Hydrogen gets added to bromine. So here since hydrogen gets added, then this will be called as reduction reaction. Bromine is going under reduction reaction. And since both are happening in the same reaction, we will call this as redox reaction. You can even check, you know, how to remember this part where hydrogen gets added, which is plus H2. And it can be thought as in terms of oxygen as minus O2. Their effect will be opposite. And we remember that removal of oxygen is termed as reduction. So addition of hydrogen is also reduction. Okay. Let's move on. This is the final equation. Manganese oxide, MnO2 reacts with HCl to give me MnCl2 plus H2O plus Cl2 chlorine. Now see over here, if I focus on manganese, manganese initially was combined with oxygen. But over the course of reaction, I see that manganese has lost its oxygen. Okay. So manganese is losing its oxygen and we know that loss of oxygen is reduction reaction. So manganese is going under reduction reaction. Now let's focus on the chlorine over here. See chlorine was attached with hydrogen. So after the reaction, if I see chlorine has lost its hydrogen, chlorine is losing its hydrogen. And we just saw over here that loss of hydrogen is oxidation reaction is similar to gain of oxygen, addition of oxygen, which is oxidation. So here chlorine is going under oxidation reaction, oxidation reaction. And since both oxidation and reduction are happening in the same reaction, this is also an example of redox reaction. And you know, when I was solving this problem for the first time, I saw that hydrogen initially was not combined with oxygen. It was combined with chlorine, right? But after the reaction, hydrogen gets combined with oxygen over here. That means I can say that oxygen is getting added to hydrogen. So can I say that hydrogen is going under oxidation? See that's a great question, but actually it's not undergoing oxidation. And you know to understand this, we will have to learn about the new definition of oxidation and reduction reaction, which is in terms of electron loss and electron gain. And you know, we have discussed about that in much detail in a separate video. So you can watch that video and you will be able to understand why hydrogen is not undergoing oxidation over here. Now one last thing, see oxidation reaction and reduction reaction, they always occur in pair, meaning if in any reaction you see something is getting oxidized, then there must be something else that is getting reduced. It wouldn't be the case that, you know, you find something is getting oxidized and there's nothing else getting reduced. They always occur in pair. See for example, if I take this reaction, carbon plus oxygen gives you carbon dioxide. So here you can see that, hey, oxygen is getting added to carbon. That's why carbon is getting oxidized. Carbon is getting oxidized, right? But you might not be able to see that what is getting reduced. However in this particular case, oxygen, this is getting reduced and I know that you might be confused. How is oxygen getting reduced? But you know, to understand this, we will have to understand the new definition of oxidation and reduction, which is in terms of loss of electron and gain of electron. And again, we have covered that in a greater detail in a separate video. So you should watch that to understand that over here. I just wanted to bring out the point that oxidation and reduction, they always happen in pair. So okay, in this video, we spoke about what are redox reactions, basically reduction and oxidation happening together and they always occur in pair. And we also saw some examples of it.