Define the term- Gelation?

Explanation

For fee z = 4
and `r=a/(2sqrt2)a=4.077xx10^(-8)cm=(4.077xx10^(-8))/(2sqrt2)=1.44xx10^(-8)cm`
Now `d=(ZxxM)/(a^3xxN_A)` here Z=4
`M=108a=4.077xx10^(-8)`
So `d=(4xx108)/((4.077xx10^(-1))^3)xx6.02xx10^(23)=10.5gm//cm^3`