That's where i am confused. There is no reference to third body.
Probably it is asking for a mixture in which there is Heat Transfer.
In my case it is (d) since reaction between water and sulfuric acid is an exothermic reaction. It could be (c) also. Not sure in both the cases.
In Carnot cycle we assume that heat addition takes place at constant temperature(temperature of system and source being same) and same is the case for Heat rejection.
But as we know that for heat flow (ie heat addition and heat rejection), temperature difference has to be there between system...
I have given enough thought to this but couldn't get anywhere.I would be glad if you express your thoughts on this.
Q:Zeroth law of thermodynamics is not valid for which one of the following,
(a) 50 ml of water at 25°C is mixed with 150 ml of water at 25°C
(b) 500 ml of milk at 15°C...