A

To match the columns:
(i) For the mixture to contain only water (Q=0) from ice at -50ºC (A), heat must raise ice to 0ºC and then melt it.
(ii) For the mixture to contain only ice (B), the steam at 100ºC would need to cool below 0ºC without melting ice.
(iii) For the mixture to contain only steam (C), sufficient energy must be present to convert water at 100ºC to steam at a higher temperature.
(iv) The final temperature is 100ºC (D) from mixing ice at 0ºC with water at 100ºC, maintaining temperature at 100ºC during phase changes.