Which of the following general reaction is an example for heterogeneous catalysis?

Match List I with List II.

List I	List II
A. Aerosol	I. Milk
B. Foam	II. Soap lather
C. Emulsion	III. Cheese
D. Gel	IV. Smoke

' $X$ ' is a protecting colloid. The following data is obtained for preventing the coagulation of 10 mL of gold sol to which 1 mL of $10 \% \mathrm{NaCl}$ is added. What is the gold number of ' $X$ '?

$$ \begin{array}{ccl} \hline \text { Expt No. } & \begin{array}{c} \text { Weight of } X \text { (in mg) } \\ \text { added to gold sol } \end{array} & \text { Coagulation } \\ \hline 1 & 24 & \text { Not prevented } \\ \hline 2 & 23 & \text { Not prevented } \\ \hline 3 & 26 & \text { Prevented } \\ \hline 4 & 27 & \text { Prevented } \\ \hline 5 & 25 & \text { Prevented } \\ \hline \end{array} $$

Which sol is used as intramuscular injection?