Bond length in H₂ molecule is 'x' nm. The covalent radius of deuterium is

Given, B.L [i.n nm]= x
The isotopes of an element differed by their masses but they have same bond lengths i.e., The bond length in H₂,D₂T₂ are same

Covalent radii [C_r]
 

${\mathrm{C}}_{\mathrm{r}}=\frac{\text{ Bond length }}{2}$

${\mathrm{C}}_{\mathrm{r}}=\frac{\mathrm{x}}{2}\mathrm{nm}$