The four quadrants and the sign of coordinates is given as follows:
Quadrant I : (n, n ) both x and y positive.
Quadrant II : ( -n,n) = x negative and y positive.
Quadrant III : ( -n,-n) = both x and y negative.
Quadrant IV: (n, -n) = x positive and y negative.
So Based on the above concept , we can say that vertex C (-n,-n) has both x and y negative and so it lies in quadrant III.
Answer is Vertex C (-n,-n)