Answer:
a)The total number of platinum atoms are
.
b)The radius of a Pt atom is 138.7 pm.
Explanation:
a) Let the total number of platinum atoms be x
And mass of x atoms of platinum be m
Edge length of platinum cube ,s= 1.0 cm
Volume of the cube = 
Density of the platinum cube = 
Mass = Density × Volume

Mass of an atom of platinum = 


b) If only 74 percent of the space inside the cube is taken up by Pt atoms.
Volume occupied by platinum atoms = 74% of 

Volume occupied by
atoms is
.



The radius of a Pt atom is 138.7 pm.