1. The problem is to rationalise the denominator of the expression $\frac{1}{\sqrt{7}}$ and express the answer in its simplest form. 2. To rationalise the denominator means to eliminate the square root from the denominator. 3. The formula used is multiplying numerator and denominator by the conjugate or the same root to get rid of the root in the denominator. 4. Multiply numerator and denominator by $\sqrt{7}$: $$\frac{1}{\sqrt{7}} \times \frac{\sqrt{7}}{\sqrt{7}} = \frac{\sqrt{7}}{7}$$ 5. The denominator becomes $7$ because $\sqrt{7} \times \sqrt{7} = 7$. 6. The expression $\frac{\sqrt{7}}{7}$ is the simplest form with a rational denominator. Final answer: $$\frac{\sqrt{7}}{7}$$