To understand how many fractions can be obtained by fractional distillation of the mixture formed by dibromination of n-butane, we need to analyze the components of the mixture and their boiling points.

Dibromination of n-butane produces a mixture of different brominated butanes. The boiling points of these brominated butanes will vary depending on the number and position of the bromine atoms attached to the butane molecule.

Here is the breakdown of the different brominated butanes and their boiling points:

1. 1-Bromobutane: Boiling point = 78.2°C
2. 2-Bromobutane: Boiling point = 99.1°C
3. 1,2-Dibromobutane: Boiling point = 129.0°C
4. 1,3-Dibromobutane: Boiling point = 146.5°C
5. 1,4-Dibromobutane: Boiling point = 172.5°C

Based on this information, we can determine the number of fractions that can be obtained through fractional distillation. Each fraction will represent a compound with a specific boiling point range.

The fractional distillation process involves heating the mixture to its boiling point and collecting the vapor that evaporates. The vapor will contain primarily the compound with the lowest boiling point. As the temperature increases, the next compound with a higher boiling point will start to evaporate and can be collected as a separate fraction.

Here are the fractions that can be obtained:

1. Fraction 1: Contains primarily 1-Bromobutane with a boiling point of 78.2°C.
2. Fraction 2: Contains primarily 2-Bromobutane with a boiling point of 99.1°C.
3. Fraction 3: Contains primarily 1,2-Dibromobutane with a boiling point of 129.0°C.
4. Fraction 4: Contains primarily 1,3-Dibromobutane with a boiling point of 146.5°C.
5. Fraction 5: Contains primarily 1,4-Dibromobutane with a boiling point of 172.5°C.

Therefore, by fractional distillation of the mixture formed by dibromination of n-butane, we can obtain a total of 5 fractions.

Hence, the correct answer is option C) 5.