1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution A lewis acid donates a electron pair while a bronsted-lowry acid accepts a proton. So I need to cancel out all the ones that has proton exchanges. They are B, C, D and E. However, in A, it isn't really an acid base reaction but a solubility equation. In B the cyanide ion accepts a proton. In C the ammonia accepts a proton. In D the water accepts a proton In E the hydroxide accepts a proton. Clearly, one of these isn't true so where was my thinking wrong? Cheers!