<prompt> The chemical used to etch enamel is:Zinc oxideMethyl methacrylatePhosphoric acidEugenol  <response>: Etchants are relatively strong acids pH 12 used to remove smear layers and to dissolve the mineral phase to allow formation of micromechanical interlocking in enamel and in dentin. A number of acidic agents have been used to produce the required microporosity. However, phosphoric acid at a concentration between 30 and 50, typically 37, is the preferred etching agent to produce consistent etching patterns while not damaging the pulp.Reference: PHILLIPS SCIENCE OF DENTAL MATERIALS, 12th ed page no 262 