B

Given: Mass of steam (m) = 1 kg = 1000 g
Temperature of steam (T_steam) = 200ºC
Temperature of water (T_water) = 100ºC
Since the entropy of steam is constant, the heat needed to convert steam at 200ºC into water at 100ºC can be calculated using the formula:
\( Q = m \cdot S \cdot \Delta T \)
where:
- Q is the heat energy
- S is the specific entropy
- \( \Delta T \) is the change in temperature
\( \Delta T = T_{steam} - T_{water} = 200 - 100 = 100ºC \)
Now substituting values into the equation:
\( Q = 1000 \cdot 0.5 \cdot 100 = 50000 \) Cal
The final answer therefore is that H = 50000 Cal.