Why it is not possible to separate the enantiomers?

Write one chemical reaction each to illustrate the following:
A coupling reaction of a diazonium salt.

Illustrate each of the following with an example of reaction:
Sandmeyer reaction.

Account for the following:
Aqueous solution of methyl amine reacts with iron (III) chloride to precipitate iron (III) hydroxide.

Illustrate  the following with an example of reaction:
Diazotization reaction.

Write one chemical reaction to explain an acylation reaction.