cetyltrimethyl ammonium bromide is type of quarternary ammonium salt how?????/

 Unlike the ammonium ion (NH₄⁺) and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged, independent of the pH of their solution. Quaternary ammonium salts or quaternary ammonium compounds (called quaternary amines in oilfield parlance) are salts of quaternary ammonium cations with an anion.Positively charged polyatomic ions of the structure NR₄⁺, R being an alkyl group or an aryl group.

Also,acetyl trimethyl ammonium  bromide is the quarternary ammonium salt having the structure-(C₁₆H₃₃)(CH₃)₃NH₄⁺Br^- , ‘4 ‘ R groups are  (C₁₆H₃₃) and ‘3’ (CH₃) groups .