At which of the following temperatures,the value of surface tension of water is minimum in $^oC$?

Surface tension may be defined as

$A$ thin metal disc of radius $r$ floats on the water surface and bends the surface downwards along the perimeter,making an angle $\theta$ with the vertical edge of the disc. If the disc displaces a weight of water $W$ and the surface tension of water is $T$,then the weight of the metal disc is:

$A$ wooden stick of length $2 \ m$ floats on water. The surface tension of water is $0.07 \ N/m$. If a soap solution with a surface tension of $0.06 \ N/m$ is applied to one side of the stick,what will be the net force acting on it in $N$?

$A$ square frame of side $L$ is dipped in a liquid. On taking out,a membrane is formed. If the surface tension of the liquid is $T$,the force acting on the frame will be (in $TL$)

Why does the free surface of a liquid tend to contract?