A block of ice at $-{10}^{°}C$ is slowly heated and converted to steam at ${100}^{°}C$. Which of the following curves represents the phenomenon qualitatively. 

Initially on heating temperature rises from $–10 {}^{o}C to 0 {}^{o}C$. Then ice melt and remains constant until all the ice melts into liquid, hence the temperature does not rise. After the whole ice has melted temperature begins to rise until reaches $100 {}^{o}C$. Then it becomes constant as, at the boiling point, the temperature will not rise.