Lady Macbeth is an example of pure ambition in the play. She, and not her husband, is the mastermind behind the plot to kill the king. Lady Macbeth comes up with the plan to murder the king once she discovers that he will be a guest in her home.
The essential appositive in the sentence "astronomer maia mitchell discovered a comet in 1847 and went on to become the first professional female astronomer in the united states," is Maia Mitchel. The last option is correct.
An appositive consists on a noun or noun phrase that renames another noun right beside it. The appositive can be a short or long combination of words.
In this particular case, the words Maia Mitchell which is a proper noun is renaming the noun astronomer, which is right before it and constitutes the subject of the sentence.
