Let C.M. be at a distance x Å from H-atom Distance of C.M. from Cl atom $= (1.27 - x) \text{\AA}$Let the mass of H-atom = m units The mass of the Cl-atom = 35.5 m units If C.M. is taken at the origin, then $mx + (1.27 - x) 35.5 m = 0$ $mx = - (1.27 - x) 35.5 m$ Negative sign indicatesthat if Cl atom is on the right side of C.M.(+), the hydrogen atom is on the left side of C.M. So, avoiding, if we get $x + 35.5x = 1.27 \times 35.5$ $36.5x = 45.085$ $x = \frac{45.005}{36.5} = 1.235 \text{\AA}$ Therefore, the centre of mass located on theline joining H and Cl nuclei at a distance of 1.24 Å from the H atom.