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

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