IDensity is calculated by mass divided by volume. As you half the Hershey bar, mass and volume change by the same proportion. Therefore, density is the same.
Wait what you answered your own question
Answer: Option (B) is the correct answer.
Explanation:
A molecules that will have more number of hydrogen bonding will has highest boiling point because to break the hydrogen bonds high heat needs to be provided.
So, in the molecule 
there is presence of two alcoholic groups. Hence, it will have strongest hydrogen bonding as compared to the rest of molecules.
In the molecule 
there will be hydrogen bonding and dipole-dipole interactions. Hence, it boiling point will be slightly less than .
In the molecule 
, there will be only hydrogen bonding. Hence, its boiling point is less than .
In the molecule 
, there is no hydrogen bonding but there will be only dipole-dipole interactions. Hence, its boiling point will be the least.
Therefore, we can conclude that increasing order of boiling point will be as follows.
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