Platinum has a density of 21 g/cm3. a platinum ring is placed in a graduated cylinder that contains water. the water level rises from 5.0 ml to 5.3 ml when the ring is added. what is the mass of the ring?

The little lump of platinum that you dropped into the graduated cylinder has

(5.3 - 5.0) = 0.3 mL = 0.3 cm³ of volume.

That's nothing but a metal shaving, a little sliver, maybe like

a 1/4-inch piece cut out of a metal paper-clip. I'm surprised

that you can read the graduated cylinder that precisely.

Its mass is

(0.3 cm³) x (21 gm/cm³) = 6.3 grams = 0.0063 kg.