Heat is supplied to water at a constant rate. Choose the correct Temperature (T) versus Heat supplied graph for water from −20°C to 120°C.

Solution:

When heat is supplied:

1. Ice warms from −20°C to 0°C → Temperature rises.
2. At 0°C melting occurs → Temperature remains constant.
3. Water warms from 0°C to 100°C → Temperature rises.
4. At 100°C boiling occurs → Temperature remains constant.
5. Steam warms from 100°C to 120°C → Temperature rises again.

Therefore the graph must contain:

• Rising line from −20°C to 0°C
• Horizontal section at 0°C
• Rising line from 0°C to 100°C
• Horizontal section at 100°C
• Rising line above 100°C

Among the given options, Graph (2) correctly represents these changes.

Answer:

Option (2)