Answer
When steam touches the surface of the body, it condenses into water. So, when steam at $100^{\circ}C$ touches the body, it releases more heat than water at $100^{\circ}C$, because extra heat energy is used to convert water to steam. So when steam condenses to water, additional heat is released which is used to convert water to steam. Thus, steam at $100^{\circ}C$ causes more serious burns than water at $100^{\circ}C$.
Work Step by Step
When steam touches the surface of the body, it condenses into water. So, when steam at $100^{\circ}C$ touches the body, it releases more heat than water at $100^{\circ}C$, because extra heat energy is used to convert water to steam. So when steam condenses to water, additional heat is released which is used to convert water to steam. Thus, steam at $100^{\circ}C$ causes more serious burns than water at $100^{\circ}C$.
