Question

How many of the following are negatively charged sols?
$Pt,Au,Ag,Fe(OH{)}_3,Al(OH{)}_3$,
$A{s}_2{S}_3,starch,clay,H_{4}Si{O}_4,eosin$,
$methyleneblue,Haemoglobin,Cu,CdS$,
$Congored,Cr(OH{)}_3$

Answer 1

Colloidal particles always carry an electric charge. This charge may be positive or neagtive.
From the data given,
Negatively charged sols are:
$Pt,Au,Ag,A{s}_2{S}_3,Starch$,
$clay,H_{4}Si{O}_4,eosin,Cu$,
$CdS,Congored$
Positively charged sols are: $Fe(OH{)}_3$, $Al(OH{)}_3$, $methyleneblue,Haemoglobin$, $Cr(OH{)}_3$