PASSAGE FOUR (Questions 8-9)
Paragraph
Uranium
1. Uranium, a radioactive metal named after the planet Uranus, is a primary source of energy in nuclear
power plants and certain nuclear weapons. It occurs n a t u r a l l y i n three different isotopes, which
d i f f e r in their facility i n undergoing nuclear fission.
2.
8A The
3.
Of these three naturally occurring isotopes o f uranium, U -238 is by far the most common, while U-235 i s
the most capable o f undergoing nuclear f i ss i o n . 9A More than 99 percent of all naturally occurring
uranium is U-238, while U-234 and U-235 each make up less than 1 percent. 9 B Nuclear fission can
occur when a U-235 nucleus is struck by a neutron, and the nucleus splits releasing energy and
releasing two or more neutrons. 9C However, nuclear fission rarely involves a U-238 or a U-234
nucleus because it is unusual for either of these nuclei to break apart when struck by a neutron. 9D
three naturally o c c u r r i n g isotopes o f uranium a r e U..234, U-235, and U-238.11 8 B Each of
these is o to p es h a s the same atomic n u m b e r o f 92, which i s the number o f protons in the
nucleus. 8 C However, each has a different n u m b e r o f neutrons a n d thus has a different atomic m a s s ,
which is the sum of the number of protons and neutrons. 8D
8. Look at the four squares [II] that indicate
where the following sentence could be
added to the second' paragraph of the
passage.
U-234 has 92 protons and 142 neutrons
for an atomic mass of 234, U ..2.35 has
92 protons and 143 neutrons for a total
of 235, and U-238 has 92 protons and
146 neutrons for a total of 238.
Where would the sentence best fit? Click
on a square [II] to add the sentence to the
passage.
9. Look at the four squares [II] that indicate
where the following sentence could
be added to the third paragraph of the
passage"
These neutrons can create a chain
reaction by causing other U-235· nuclei
to break up.
Where would the sentence best fit? Click
on a square [Ill to add the sentence to the
passage.
Answer key 8 D, 9 C