The simplified form of $\sqrt{72}$ is $6\sqrt{2}$.

To simplify $\sqrt{72}$, we begin by determining its prime factors. We can break down $72$ as follows:

Next, we can group the prime factors in pairs, resulting in:

$(2 \times 2) \times (3 \times 3) \times 2.$

Each pair of identical factors can be taken out of the square root as a single number. Therefore, we have:

This indicates that the square root of $72$ can be expressed as $6$ times the square root of $2$.

The technique of simplifying square roots by factoring them into prime numbers and then grouping pairs is a valuable skill in GCSE Maths. This method allows for the transformation of complex square roots into simpler forms, making them easier to handle in subsequent calculations.