The correct option is C x2+y2=1
Let mid point be P(h,k)
and origin be O(0,0) which is also centre of the given circle.
Since chord making right angle at origin and P is mid point, OP will bisect the right angle.
⇒OP=rcos45∘ where r is radius of the given circle.
⇒OP=√(h−0)2+(k−0)2=√2×1√2=1
Squaring we get, h2+k2=1
Hence locus of P(h,k) is, x2+y2=1