J.R. S. answered 12/30/18
Ph.D. University Professor with 10+ years Tutoring Experience
I answered this before and to know which is an acid and base, you need to memorize certain things. There are different definitions of acids and bases but in beginning chemistry, you can think of an acid as something that dones a proton (H+) and a base as something that donates OH- . So in B, HNO3 is the acid (it dones H) and KOH is the base (it donates OH). The H from acid and the OH from base makes HOH which is the same as H2O or water.