The old mansion stood on the hill, its windows staring out like vacant eyes, and a sense of profound ______ hung in the air.
Correct: C
The imagery of 'vacant eyes' in an 'old mansion' on a hill suggests abandonment, decay, and a somber atmosphere. 'Desolation' conveys a strong sense of emptiness, ruin, loneliness, and abandonment, which perfectly matches and enhances the eerie and isolated mood established by the preceding description. 'Quietness,' 'peace,' and 'stillness' are too neutral or positive to fit the intended tone.