c. units of volume to units of
length.
d. units of length to units of
volume.

13.A student determined the density of
aluminum by averaging the
results of three density
calculations. Each value was
different, but the average was
equal to the accepted value for
aluminum's density. The results
of this investigation are best
described as
a. accurate, but not precise.
b. precise, but not accurate.
c. both precise and accurate.
d. neither precise nor accurate.

14. Neutral atoms contain equal numbers
of
a. electrons and neutrons.
b. protons and neutrons.
c. protons and electrons.
d. protons, electrons, and
neutrons.

15. An atom of potassium has 19 protons
and 20 neutrons. Its mass
number is
a. 9.
b. 19.
c. 20.
d. 39.

16. The isotope uranium-235 has 92
protons and 143 neutrons.
Therefore, its mass number
a. 92.
b. 235.
c. 143.
d. impossible to determine.