What is the mass of 5.33×1021 platinum atoms

To find mass of a bunch of atoms, we first have to convert to moles (using Avogadro's number), then the atomic mass (from the periodic table):

5.33 x10^21 atoms Pt x (1 mole/6.022x10^23 atoms) x (195.08 grams Pt/1 mole)
= 1.73 grams of Pt

Notice the answer has three digits - three significant figures since the 5.33 has three sig figs - the fewest of all the values in the problem.

That result from subduction of oceanic plates beneath lighter continental plates. most of the earth's volcanoes are located around the pacific ring of fire because that the location of most of the earth's subduction zones.