Why is the coefficient of static friction considered a property of the surfaces in contact?

$A$ block of mass $4 \text{ kg}$ is placed on a horizontal surface having coefficients of static and kinetic friction as $0.5$ and $0.4$ respectively. If a force of $4 \text{ N}$ is applied parallel to the horizontal surface, then the force of friction acting on the body will be $\left[g = 10 \text{ m/s}^2\right]$ (in $\text{ N}$)

$A$ force of $98 \, N$ is required to just start moving a body of mass $100 \, kg$ over ice. The coefficient of static friction is

As shown in the figure, a block of mass $10 \ kg$ lying on a horizontal surface is pulled by a force $F$ acting at an angle $30^{\circ}$ with the horizontal. For $\mu_{s} = 0.25$, the block will just start to move for the value of $F$: [Given $g = 10 \ ms^{-2}$] (in $N$)

If a ladder weighing $250\,N$ is placed against a smooth vertical wall and the coefficient of friction between the ladder and the floor is $0.3$,what is the maximum force of friction available at the point of contact between the ladder and the floor?

$A$ force $F = mg$ is acting on a block of mass $m$ at an angle $\theta$ with the horizontal. The coefficient of friction between the block and the surface is $\mu$. The block can be pulled along the surface if: