Which of the processes described below are irreversible?
(a) The increase in temprature of an iron rod by hammering it.
(b) A gas in a small cantainer at a temprature T1 is brought in contact with a big reservoir at a higher temprature T2 which increases the temprature 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.