Which is there more of on Earth, rock or water?

Definitely more rock than water, either in the crust, or the whole
planet.  Even though water is found as a component in most minerals,
the bulk of the earth is silicon based.

Hmmm.  If one reads the question literally, " . . . more of ON earth,
. . ." (emphasis added), isn't it true that 70% of the earth's surface
(" . . . ON earth, . . .] is covered with water?

Yea, it really depends what you mean on this one.

If you are asking about the Earth's surface, then there is more water
on the earth's surface than there is land.  70% or so of the Earth's
surface is covered with water; the other 30% being land of course.

If you are talking about the Earth as an entire planet, then it is
mostly, well, earth, or rock.

It would seem that the answer would be rock as the earth's crust is
rock and "carries" the many bodies of water on top of it. The crust is
about 20 miles thick on land and 4-7 miles under oceans. However,
below the earth's crust to the mantle and the core we have no idea how
much water or other liquids could be found there. The mantle is a
thick layer of rock below the earth's crust. It is about 1,800 miles
deep. The solid rock in the mantle is made of silicon, oxygen,
aluminum, iron, and magnesium. It is mostly a solid silicate rock. The
core is made of liquid molten nickel and iron.

Consider that the American NSF found a deep underground (but still
within the crust) water sea at Lake Voshtok Antartica. How many more
are down there? I'll go with ROCK..

Spooky