The correct answer is C) angle of the cone. The last two digits stamped on a fuel oil atomizer sprayer plate represent the cross-sectional area ratios of the tangential slots and orifice. This ratio determines the angle of the cone of the oil spray, which is a critical factor in the performance and efficiency of the atomizer. A higher ratio results in a narrower spray cone, while a lower ratio produces a wider spray cone. The angle of the cone directly affects the degree of atomization, but it is not the same as the degree of atomization itself, which is why option D is incorrect. The capacity of the atomizer (option A) and the density of the oil spray (option B) are not directly determined by the cross-sectional area ratio on the sprayer plate.