How do limestones that begins as a coral be found on land?

The limestone began to form millions of years ago, when the land was under the ocean. The rock developed from shells of tiny organisms that float in the ocean. ... However, in the case of reefs, the limestone is produced directly as coral organisms build their skeletons one on top of another.

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.