For laminar flow over a flat plate, the thickness of the boundary layer at a distance from the leading edge is found to be 5 mm. The thickness of the boundary layer at a downstream section, which is at twice the distance of the previous section from the leading edge, will be

1. 10 mm

2. \(5\sqrt 2 mm\)

3. \(\frac{5}{{\sqrt 2 }}mm\)

4. 2.5 mm