1.sir in that image.....why 10 has been used...what is it?

2.work done is maximum inreversible isothermal expansion ..why?

(1)At the final stage the equlibrium pressure is 1 atm and the volume is =10lt
therefore work done= -2.303nRT log(V2/V1)
=-2.303*.1*10log(10/2) =16.1 lt atm
because PV=nRT
(2)maximum work is done in reversible isothermal expansion
If a process does work on the surroundings, you get more work out of the process if it is done slowly. This is because less heat is lost to the surroundings. So a reversible process (infinitely slow) does the maximum work. There is one example : the work done by a gas expanding inside a piston. We will see that the maximum amount of work is obtained when the gas is allowed to expand very slowly (reversibly).
If a process does work on the surroundings, you get more work out of the process if it is done slowly. This is because less heat is lost to the surroundings. So a reversible process (infinitely slow) does the maximum work. There is one example of this that is easy to understand: the work done by a gas expanding inside a piston. We will see that the maximum amount of work is obtained when the gas is allowed to expand very slowly (reversibly).