In a methane $\left({\mathrm{CH}}_4\right)$ molecule each hydrogen atom is at a corner of a regular tetrahedron with the carbon atom at the centre. In coordinates where one of the C-H bonds is in the direction of $\widehat{\mathrm{i}}+\widehat{\mathrm{j}}+\widehat{\mathrm{k}}$, an adjacent C-H bond is in the $\widehat{\mathrm{i}}-\widehat{\mathrm{j}}-\widehat{\mathrm{k}}$ direction. Then angle between these two bonds.

• A

  ${\cos }^{-1}(-\frac{2}{3})$

• B

  ${\cos }^{-1}\left(\frac{2}{3}\right)$

• C

  ${\cos }^{-1}(-\frac{1}{3})$

• D

  ${\cos }^{-1}\left(\frac{1}{3}\right)$