Silver iodide is used for producing artificial rain because $AgI$

Colloidal solution of gold is prepared by .............

The coagulation of $100 \, mL$ of a colloidal sol of gold is completely prevented by the addition of $0.25 \, g$ of a substance '$X$' to it before adding $10 \, mL$ of $1 \% \ NaCl$ solution. The gold number of '$X$' is:

Gold numbers of some colloids are: Gelatin $0.005-0.01$,Gum arabic: $0.15-0.25$; Oleate: $0.04-1.0$; Starch: $15-25$. Which among these is a better protective colloid?

Various types of colloids are given below. Match Column $X$ with Column $Y$.

$X$ (Colloid)	$Y$ (Classification)
$I$. Smoke	$A$. Sol
$II$. Gelatin	$B$. Aerosol
$III$. Soap lather	$C$. Emulsion
$IV$. Milk	$D$. Foam

The gold numbers of $A, B, C$ and $D$ are $0.04, 0.002, 10$ and $25$ respectively. The protective power of $A, B, C$ and $D$ are in the order: