Correct Answer - Option 3 : (Grain size)
2
Explanation:
The coefficient of permeability (k) is given as;
\(k = C \times \left( {\frac{{{\gamma _w}}}{\mu }} \right) \times \left( {\frac{{{e^3}}}{{1 + e}}} \right) \times {D^2}\)
where
D = grain size of soil particles
So, permeability is directly proportional to the square of grain size.