In which reaction is precipitation occurring? a. mgcl2(aq) cuso4(aq) → cucl2(aq) mgso4(aq) b. cdso4(aq) k2s(aq) → cds(s) k2so4(aq) c. naoh(aq) nh4cl(aq) → nacl(aq) nh4oh(aq) d. k2so4(aq) naoh(aq) → k2oh(aq) naso4(aq) e. hno3(aq) koh(aq) → kno3(aq) h2o(l)