Chemistry question helppp

What type of reaction is used to convert (CH3)3N into the cationic surfactant [(CH3)3N(CH2)15CH3]Cl?
A. Bronsted–Lowry acid-base
reaction
B. Nucleophilic addition
C. Nucleophilic
addition-elimination
D. Nucleophilic substitution
the answer is D and I do not understand why and by any chance what are we substituting to get the required result, does HCl have to be involved, and KCN to increase the number of c atoms but I'm not sure

What type of reaction is used to convert (CH3)3N into the cationic surfactant [(CH3)3N(CH2)15CH3]Cl?
A. Bronsted–Lowry acid-base
reaction
B. Nucleophilic addition
C. Nucleophilic
addition-elimination
D. Nucleophilic substitution
the answer is D and I do not understand why and by any chance what are we substituting to get the required result, does HCl have to be involved, and KCN to increase the number of c atoms but I'm not sure

Whilst it is good you have understood that cyanide can sometimes be used to increase carbon chain lengths, it isn’t useful to consider in this case as (CH3)3N is neither a haloalkane nor an aldehyde/ketone - it’s an amine and so you cannot increase its chain length with cyanide.
One important feature of amines is that the nitrogen has a lone pair and so it can act as a nucleophile. What families of organic molecules can react with nucleophiles and what sorts of mechanisms and products do you get?

Do you know what the other (i.e. not the (CH3)3N reactant is?

acyl chlorides can react with nucleophiles, the mechanism is Nucleophilic addition-elimination and the products could be carboxylic acid, ester, primary amides or secondary amides

That’s one possible kind of molecule that can react with nucleophiles, though after the addition, you’d still have an oxygen attached when the product given in the question does not, so maybe try another family of molecules that lacks an oxygen.
Hint: re-read my first post. Cyanide is also a nucleophile so surely some of the kinds of molecules it can react with also might work?

ok my best try is that cyanide reacts with halogenoalkanes in nucleophilic substitution to form nitriles so could it be that the (CH3)3N reacted with a Cl containing halogenoalkane? I think I am wrong still because you said earlier that (CH3)3N is neither a haloalkane nor an aldehyde/ketone

Indeed, the molecule (CH3)3N reacts with in this case is a chloroalkane.

yayyy! I am so glad I got the explanation thank you very much for your help and patience. I also want to use this opportunity to show my appreciation as you have helped me so many other times in other different threads. I find the student room team amazing, the help provided is unmatched and I will ever be so grateful!