[spas105]

So in my o chem lab we reduced vanillin with NaBH4...then we used HCl to decompose excess NaBH4.Is this decomposition a reduction of NaBH4 or oxidation ?  Thanks!

[voidSetup]

NaBH₄ is a reducing agent so it gets oxidized in the reaction.  It gets oxidized when it reduces vanillin also, but afterward you want to neutralize any that is left with HCl

[Vidya]

Acids are used in reduction reactions for protonation

[AWK]

First off all write down and balance this decomposition reaction. Then you find that formally H^- reacts with H⁺ forming H₂ with null oxidation number. Hence this is a normal redox reaction. What is oxidized, what is reduced - just use definitions of oxidation and reduction.
hint
NaBH₄ + HCl + H₂O = NaCl + H₃BO₃ + H₂