The correct answer is C) 5.0. The mechanical advantage of a tackle, which is a system of ropes and pulleys used to lift or move heavy loads, is determined by the number of rope parts supporting the load. In the case of tackle number 10, the illustration shows a 5-part tackle, which has a mechanical advantage of 5.0. This is because the load is supported by 5 rope parts, resulting in a mechanical advantage of 5.0. The other options are incorrect because A) 4.0 is the mechanical advantage of a 4-part tackle, B) 4.5 is not a common mechanical advantage for a tackle, and D) 5.5 does not match the 5-part configuration shown in the illustration.