Answer:
To convert 100.0 g of water at 20.0 °C to steam at 100.0 °C requires 259.5 kJ of energy. Let me know if this helped?
Answer:

when there is a radical in the denominator, we should rationalize (mutiply the denominator and numerator by the radical) to get rid of the radical in the denominator.
Oxygen had 6 valence electrons