What is difference between tempering and aging?

What kind of ion is contained in salts that produce an acidic solution? a positive ion that attracts a proton from water a positive ion that releases a proton to water a negative ion that attracts a proton from water a negative ion that releases a proton to water

Iknow #2 is d. i just need to know why

Which traits do human embryos have that link them to a common ancestor with fish and reptiles? a. scales and tail b. gill slits and scales c. tail and gill slits d. hair and tail