Which of the following is not a surface phenomenon?

The quenching of fluorescence depends on:

$A$ cube of edge length $1 \ cm$ is divided into smaller cubes of uniform size of length $1 \ nm$. Assuming that no voids are present, the ratio of total surface area of all the cubes of $1 \ nm$ edge length to the surface area of the initial cube is

Sodium thiosulphate is used in photography to :-

Identify the correct statement$(s)$ from the following:
$a$) Protective power of a lyophilic sol is more if its gold number is more
$b$) In the coagulation of negative sols,the coagulating power of cations follow the order $Na^{+} > Ba^{2+} > Al^{3+}$
$c$) Cloud is a solid in gas type of colloid
$d$) Physical adsorption is non-specific and multilayered at high pressure.

Adding soap to water ................