Out of water and steam, which will possess more energy at 100^oC?

Steam

The correct answer is option 2. Steam.

In an open system at 100°C, steam will possess more energy than water. This is because steam has undergone a phase transition from water, and during this process, heat energy has been added to convert the water at 100°C into steam without a change in temperature.

When water reaches its boiling point (100°C at standard atmospheric pressure), further addition of heat energy leads to the phase transition from liquid water to steam. The energy added during this phase transition is known as the latent heat of vaporization.

In contrast, liquid water at 100°C has not undergone this phase transition and, therefore, possesses less energy than the steam coexisting with it.