Which of the following is not an acid-base neutralization reaction?
nh3 + hcl yields nh4cl
h2 + br2 yields 2 hbr
hcl + hbr yields h2 + clbr
2 hbr + ca(oh)2 yields cabr2 + 2 h2o

A neutralization process is a reaction between an acid and a base which yields a salt and water. From the choices, a neutralization reaction would be: 2 HBr + Ca(OH)2 yields CaBr2 + 2 H2O.  Moreover, NH3 + HCl yields NH4Cl is also a neutralization reaction. The complete reaction is actually NH4OH + HCl --> NH4Cl + H2O. NH4OH is the aqueous solution of NH3. This reaction is still a neutralization reaction.

On the other hand, the reaction HCl + HBr yields H2 + ClBr is not valid. There is no reaction between HCl and HBr because both are strong acids. They would just dissociate into ions like H+, Cl- and Br-.

The valid reaction that is clearly not a neutralization process is H2 + Br2 yields 2 HBr. This is a combination reaction yielding a strong acid HBr.