An element 'X' (At. Mass = 40 g `mol^(-1)`) having f.c.c structure has unit cell edge length of 400 pm . Calculate the density of 'X' and the number of unit cells in 4 g of 'X' .
`(N_(A) = 6.022 xx 10^(23) mol^(-1))`.

Explanation

To solve the problem, we will follow these steps:

### Step 1: Determine the number of atoms per unit cell (z) for FCC structure.
In a face-centered cubic (FCC) structure, there are:
- 8 corner atoms, each shared by 8 unit cells (contributing 1 atom)
- 6 face-centered atoms, each shared by 2 unit cells (contributing 3 atoms)

Thus, the total number of atoms per unit cell (z) is:
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