21.46 g/cm³
Further explanation
This calculation pertains to the topic of the arrangement of crystalline solids.
This question requires us to determine the theoretical density of platinum (Pt).
The formula for calculating theoretical density can be expressed as 
using the following symbols, i.e.,

The given information includes:
an atomic radius of 0.1387 nm; therefore, 
Consequently, 
the atomic mass is 195.08 g/mol
Since platinum exhibits an FCC crystal structure, n = 4 atoms, and 
Now, let’s calculate the unit cell volumes.



Insert all data into the general formula.

Therefore, the theoretical density of platinum equates to 21.46 g/cm³ (rounded to two decimal places).
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Keywords: platinum, Pt, the FCC crystal structure, atomic radius, weight, mass, theoretical density, volume, face-centered cubic