In the C–X bond, the bond length varies with a change in the size of the halogen atom. The strength of this C–X bond decreases as the size of the halogen atom (X) increases due to the increase in the size of the p-orbital of that atom. That is why the p-orbital becomes more diffused and the chances of overlapping with the orbital of the carbon atom deteriorate. Due to this, the C–X bond is elongated and has low strength.