A sample of HCl gas is placed within an electric field of 2.5 ×...

The torque acting on an electric dipole in a uniform electric field is given by $\tau = pE \sin \theta$, where $p$ is the dipole moment, $E$ is the electric field, and $\theta$ is the angle between the dipole moment and the electric field.

The torque is maximum when $\theta = 90^{{}^{{}^{\circ}}}$, which gives $\sin \theta = 1$.

\tau_{\text\max} = pE

Given:
$p = 3.4 \times 10^{-30} \text{ C m}$
$E = 2.5 \times 10^4 \text{ N C}^{-1}$

Substituting the values:
\tau_{\text\max} = (3.4 \times 10^{-30}) \times (2.5 \times 10^4)

\tau_{\text\max} = 8.5 \times 10^{-26} \text{ N m}