Question

Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $SnC{l}_2$, formaldehyde, phenyl hydrazine, etc.
2$AuC{l}_3$ + 3$SnC{l}_2$ $\to$ 3$SnC{l}_4$ + $2A{u}_{sol}$
The above method is an example of:

• A. reduction method
• B. oxidation method
• C. hydrolysis method
• D. double decomposition method

Answer 1

The correct option is A reduction method

• A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
  
• Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $SnC{l}_2$, formaldehyde, phenylhydrazine.
  

In the given reaction,

$2AuC{l}_3+3SnC{l}_2\to 3SnC{l}_4+2A{u}_{sol}$

The oxidation state of $Sn$ is changing from -2 to -4. So,it is gaining electrons and hence the method is the reduction method.