Which of the processes described below are irreversible ?
    a)    The increase in temperature of an iron rod by hammering it    
    b)    A gas in a small container at a temperature T₁ is brought in contact with a big reservoir at a higher temperature T₂ which increases the temperature of the gas
    c)    A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston
    d)    An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas

• A

  only a, b are correct   

• B

  only b, d are correct

• C

  only c, d are correct   

• D

  a,b,d are correct