The formula for borax is Na2B4O7.10H2O. The number of water molecules
in two moles of borax formula units is:
a. 6.02 x 10 23
b. 10 
c. 1.20 x 10 25
d. 20

Hi, teatea-ga:

After I posted my comment, tutuzdad-ga graciously insisted (over my
objection) upon having the original answer removed and asked that I
post a fully corrected solution in its place.

A mole is by definition a certain number (Avogadro's number, 6.022e23
to be precise) of independent units, usually molecules of a chemical
substance.  Here the units include a "water of hydration" in addition
to the borax substance, consisting of 10 molecules of H2O associated
with Na2B4O7.

Two moles of borax formula units would then contain twenty moles of
water.  But the question asks for the number of "molecules" of water. 
So the answer is, as noted in the comment below:

20 * 6.02e23 = 1.20e25 molecules

Thus C. is the correct answer here.

I hope that this "switcheroo" on the answer may help in some way to
clarify the procedure for working these kinds of problems.

regards, mathtalk-ga

With all due respect for the basic concept espoused by tutuzdad-ga in
answering the question, the wording asks for "the number of water
molecules".  Therefore the 2 moles of borax formula units, which
contain as tutuzdad-ga points out 10 molecules of water per unit,
contain 20 moles of water.  To translate this into a "number of water
molecules" we must multiply by Avogadro's number:

20 x 6.02E23 = 1.20E25

The correct multiple choice answer was C.

regards, mathtalk-ga