Why is the metal gold often found as the metal in the ground?

13) a 14) a15) b16) i don't know sorry17) a (maybe)

Pretty sure it's d. heterogeneous is separated by physical properties. 

D=m/v =57.9/3 = 19.3 g/cm^3

According to arrhenius theory of acid and bases, an acid is a proton donor, while base donates hydroxyl ions. further, acid and base reacts to form salt and water.consider following example.hcl    +      h2o          →      cl-          +      h3o+here, hcl has donated a proton, hence it is an acid.now consider following reactionhcl      +      naoh            ↔      nacl      +        h2oin this reaction, hcl donates proton, hence it is acid. on other hand, naoh donates hydroxyl ion (i.e. hence it is a base.