Which of the following processes does $NOT$ result in coagulation?

Colloidal $Fe(OH)_3$ and colloidal gold are positively and negatively charged sols,respectively. Which of the following statements is $NOT$ correct?

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

Which of the following has the minimum coagulating power?

Curdling of milk is caused due to the formation of which of the following acids by the bacteria?

$A$ colloidal system in which gas bubbles are dispersed in a liquid is known as