 I will write one reaction here you have to write down the cell notation. Suppose the reaction is this 2Ag plus H2 gas we have then we have 2H plus Aq plus 2Ag sorry this is the reaction we have to write down the cell notation. The reaction of L1 is what? H2 right so we will write H2 gas it is 2H plus plus 2Aq and capital reaction is what? Aq plus 2Aq gives 2Ag however this is not required here. So we have a solid bridge right the anode capital reaction is not required just we need to identify. This is anode and another one is partial pressure we have to mention H2 is converting into H plus right so we will write H2 gas converts into H plus C1 molar suppose the concentration is minus. And here we have to mention what? The pressure of it right so H2 pressure suppose I am assuming B atmosphere. After this we have got Ag plus converting into Ag so we have Ag plus concentration is suppose C2 molar then we have phase boundary Ag solid then we have got this is the cell notation. But one important thing here it is what? Since it is a gaseous substance right so for gaseous substance we have to provide a surface where the reaction takes place right so we have to introduce an inert electrode and then we will use platinum. So whenever you have a gaseous substance we have to add an inert electrode onto it so that at that surface the gas will react with the ion part of the electron okay. So whenever you have gaseous substance you must have to add this any inert electrode generally we use that. This is the cell notation of this reaction right this we must remember. Understood right so this is how we write down the cell notation of cell reaction. Now if cell notation is given can you write down the cell reaction is it? So for cell notation what you can conclude first of all you have to write down the reaction of anode and cathode and then you have to add both to get the net reaction. So whatever written in the left hand side that will represent what? Anode and this one is that is one example of that also okay. H plus 6 it means the balance reaction we don't write here. We will just write down the atoms ions right when you write down the reaction like this then you have to write this okay. So one will see which cell notation how to write down the cell reaction. The cell notation is given here the cell condition is this A g solid if A g plus aqueous concentration not even you can assume see what is going on right and then it gives C u 2 plus aqueous C u solid E c. We have to write down the cell reaction okay write down the reaction of anode reaction of cathode and then write down the net reaction. Then one more thing cell rotation is given back in the C l minus C l minus aqueous concentration A g plus aqueous solid E c. This is C 2 and this is C l minus C l. Then what is the reaction of anode since the cell notation so this is anode so the reaction of anode is what A g solid gives A g plus plus an electron and the next reaction is C u 2 plus plus 2 electron gives C u solid aqueous aqueous. So when you add these to the number of electrons must get cancelled right so we have to multiply this reaction by 2 and when you add this electrons get cancelled 2 A g solid plus C u plus 2 aqueous gives 2 A g plus aqueous C u number of electron exchange what is the number of electron exchange 2 electron the electron which gets cancelled is the number of electron exchange right similarly this one is anode so the reaction of anode is what C l minus aqueous gives C l 2 plus you multiply by 2 chlorine and number of charge both are like this right yes similarly what you write A g plus plus 1 electron gets A g solid this is also A g again to cancel the electron we have to multiply by 2 when you add this the reaction becomes 2 C l minus plus 2 A g plus gives C l 2 gas plus 2 A g solid this is the reaction so conversion of cell rotation into cell reaction and cell reaction to cell rotation is important we will have this application when you solve that problem ok. Now the next we have to understand this the calculation of right on next the calculation of relative standard electron rotation relative standard electron rotation why we are calling it as relative standard electron see a half cell does not work alone right if half cell does not work alone we cannot find out the absolute value of that particular half cell right so with what we do we assume the half cell of one electrode like the electrode potential of one half cell and that half cell is what hydrogen standard hydrogen electron so what we assume the standard electrode potential of S H E S H E is called standard hydrogen electrode is 0 right and with respect to that we will calculate the electrode potential of other half cells suppose you have to find out for copper right what we do we will take copper half cell we will connect this with a voltmeter and this side we have got hydrogen in it right this is hydrogen this is copper right so since we have assumed this for 0 so what is the A half of the cell E cell is what E cathode minus E N O E of copper minus E of hydrogen so this deflection in this voltmeter gives you this E cell right E cell you have got right E of hydrogen in this volt we assume 0 so we will get the value of E of copper similarly in this way only we calculate the reduction potential of various electrodes copper, zinc, iron, lithium, sodium many others right so we will get the value of electrode potential for different electrodes when we arrange this in ascending or descending order we get a series and that series because it is what? Electrochemical series correct so we will see why we call it as relative because we are calculating the reduction potential of one electrode with respect to that side is a relative standard electrode right so that is standard electrode that we are taking for this purpose is what? Standard hydrogen right so this since the half cell does not work alone since the half cell does not work alone hence we cannot calculate since the half cell does not work alone hence we cannot calculate the absolute value of the absolute value of reduction potential for any electrode the reference electrode for this purpose is standard hydrogen electrode standard hydrogen electrode