Which one of the sols acts as a protective colloid?

Which of the following salt solutions would coagulate the colloid solution formed when $FeCl_{3}$ is added to $NaOH$ solution,at the fastest rate?

Which of the following electrolytes has the maximum coagulation power for $As_2S_3$ sol?

The correct statements with respect to dialysis of colloidal solution are
$I$. Colloidal particles can pass through the membrane.
$II$. Animal bladder can be used as membrane.
$III$. Cellophane is not used as membrane.
$IV$. Ions or small molecules can diffuse through membrane into water.

When a strong beam of light is passed through a colloidal solution,the light will

Why does leather get hardened after tanning?