Why the temperature of all bodies remains constant at room temperature?

In semiconductor at a room temperature

Which is not stable at room temperature ?

A Carnot engine whose low-temperature reservoir is at 350 K has efficiency of 50%. It is desired to increase this to 60%. It the temperature of the low-temperature reservoir remains constant, then the temperature reservoir remains constant, then the temperature of the high-temperature reservoir must be increased by how many degrees?

Can the temperature of an isolated system remain constant?

In a permamnent magnet at room temperature

Which is solid at room temperature