Which is true of transition metals when moving from left to right on the periodic table?
the d sublevels are not filled across the period.
the cation radii become larger across the period.
atomic radii increase slightly and then start to decrease.
atomic radii decrease slightly and then start to increase.

The correct option is D.

Transition metals are those metallic elements that are located in the central block of the periodic table. They exhibit various valency states and they generally have various colors. The atomic radius of an element refers to the measure of the size of its atom. For transition metals, their atomic radii decrease slightly and then start to increase, when one is moving from the left to the right of the periodic table.

they are all solids.