In the following reaction for the preparation of gold sol,$a, b, c, x, y$ and $z$ are $a AuCl_3 + b HCHO + c H_2 O \longrightarrow x Au (\text{sol}) + y HCO_2 H + z HCl$. Find the correct values for the coefficients.

• A
  $a=2, b=3, c=3, x=2, y=3, z=6$
• B
  $a=2, b=3, c=2, x=2, y=3, z=4$
• C
  $a=2, b=2, c=2, x=2, y=2, z=4$
• D
  $a=3, b=2, c=2, x=3, y=2, z=6$