Four particles, each of mass 1 kg are placed at the corners of a square OABC of side 1 m. ‘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

  $\widehat{\mathrm{i}}+\widehat{\mathrm{j}}$

• B

  $\frac{1}{2}(\widehat{\mathrm{i}}+\widehat{\mathrm{j}})$

• C

  $(\widehat{\mathrm{i}}-\widehat{\mathrm{j}})$

• D

  $\frac{1}{2}(\widehat{\mathrm{i}}-\widehat{\mathrm{j}})$