The softening point of bitumen refers to the temperature at which it transitions from a hard, solid state to a more fluid or soft state. This temperature is important because it determines the material's ability to withstand heat during application, particularly in road construction where bitumen is used for asphalt.
Bitumen is a complex mixture of hydrocarbons, and its softening point is an indicator of its thermal stability and viscosity. The softening point is determined by heating a sample of bitumen in a specific method, such as the ring and ball test, until the bitumen begins to soften and flow.
As the sample is heated, the temperature at which bitumen softens and flows is recorded. The unit of measurement for the softening point is therefore temperature, typically measured in degrees Celsius (°C) or Fahrenheit (°F).
Hence, the softening point of bitumen has the same unit as that of temperature, which corresponds to option (B).
Final Answer: temperature