The ability of an ion to bring about coagulation of a given colloid depends upon

The stability of lyophilic colloidal sol is due to

$A$ $42.12 \% (w/v)$ solution of $NaCl$ causes precipitation of a certain sol in $10 \, hours$. The coagulating value of $NaCl$ for the sol is $.....$
[Given : Molar mass : $Na = 23.0 \, g \, mol^{-1} ; Cl = 35.5 \, g \, mol^{-1}]$

When $FeCl_3$ is added to an excess of hot water,it gives a sol '$X$'. When $FeCl_3$ is added to $NaOH_{(aq)}$ solution,it gives a sol '$Y$'. The sols '$X$' and '$Y$' formed in the above processes respectively are:

Given below are two statements:
Statement $I :$ Emulsions of oil in water are unstable and sometimes they separate into two layers on standing.
Statement $II :$ For stabilisation of an emulsion,excess of electrolyte is added.
In the light of the above statements,choose the most appropriate answer from the options given below:

In which of the following is the Tyndall effect not observed?