In which section of the Declaration of Independence is the purpose of government described?

the introduction

the body

the conclusion

the grievances

The correct answer is the the introduction

This is where the idea as to why it was written and what its purpose is was explained. The body contained the grievances that were about the bad things that the king did and why it wronged people of the colonies, while the conclusion was in the end and as such did not have a place for the purpose which is in the beginning.

It would be in the "introduction" or the "preamble" where the purpose of government is described in the Declaration of Independence, since this is where Jefferson wanted to make it clear why exactly the colonies were declaring their independence.