Four particles, each of mass `1kg` are placed at the corners of a square `OABC` of side `1m`. `O` is at the origin of the coordinate system. `OA` and `OC` are aligned along positive X-axis and positive Y-axis respectively. The position vector of the centre of mass is (in `m`)
A. `hati+hatj`
B. `1/2(hati+hatj)`
C. `(hati-hatj)`
D. `1/2(hati-hatj)`