AnswersAA-F26 Physical ScienceRadioactivity

Radioactivity — Unit test Answers

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Atoms of arsenic (As) are often added to silicon (Si) in a process called doping to change the conductivity of the silicon. How does the addition of arsenic change the conductivity of silicon?

A
An atom of arsenic has one fewer valence electron and more electron shells than an atom of silicon, so the conductivity decreases because the arsenic atom gains an electron.
B
An atom of arsenic has one more valence electron and more electron shells than an atom of silicon, so the conductivity decreases because the arsenic atom loses the electron.
C
An atom of arsenic has one fewer valence electron and fewer electron shells than an atom of silicon, so the conductivity increases because the arsenic atom gains an electron.
D
An atom of arsenic has one more valence electron and more electron shells than an atom of silicon, so the conductivity increases because the arsenic atom loses the electron.
2
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Calcium, magnesium, and strontium are near each other on the periodic table and have some characteristics in common, but they differ in chemical reactivity. Which lists these metals in order from most reactive to least reactive?

A
calcium, magnesium, strontium
B
magnesium, calcium, strontium
C
strontium, calcium, magnesium
D
strontium, magnesium, calcium
3

An atomic physicist determines that an atom is composed of 8 positively charged particles and has a mass of 15 amu. Which is the best conclusion that can be drawn?

A
The atom has 7 neutrons and 8 protons.
B
The atom has 7 electrons and 8 protons.
C
The atom has 8 neutrons and 7 electrons.
D
The atom has 8 electrons and 7 protons.
4

Which element is most likely to carry electric current easily?

A
tin (Sn)
B
sulfur (S)
C
antimony (Sb)
D
selenium (Se)
5

Which is the property of nonmetals to evaporate easily?

A
brittle
B
dense
C
liquid
D
volatile
6

Who was the first chemist to organize elements by atomic number?

A
Johann Wolfgang Döbereiner
B
Antoine Lavoisier
C
Henry Moseley
D
John Newlands
7

Sonya is studying a nonmetal element. She learns that the element is like other elements in its group because it can bond to form a salt or an acid. She also learns that the element is the most reactive element in its group. Which element is Sonya most likely studying?

A
sulfur (S)
B
neon (Ne)
C
fluorine (F)
D
iodine (I)
8

This is how manganese appears in the periodic table.

Question illustration
A
period symbol of manganese
B
isotope symbol of manganese
C
group symbol of manganese
D
chemical symbol of manganese
9

A sample is in the second half-life. What percent of the sample is stable at this point?

A
12.5%
B
25%
C
50%
D
75%
10

Which radioactive isotopes did the Curies discover?

A
polonium and radium
B
radium and carbon-14
C
carbon-14 and uranium
D
uranium and polonium
11

Atoms of two different elements must have different

A
electrical charges.
B
numbers of neutrons.
C
atomic numbers.
D
energy levels.
12

These models show the electron structures of two different nonmetal elements.

Question illustration
A
Element 1 is more reactive because it has fewer electron shells and is toward the top of its group on the periodic table.
B
Element 1 is more reactive because it has more electrons in its valence shell and is farther to the right on the periodic table.
C
Element 2 is more reactive because it does not have a valence shell close to the nucleus, so it will attract electrons.
D
Element 2 is more reactive because it does not have a full valence shell, so it will attract electrons.
13

An atom of the element chromium has an atomic number of 24 and a mass number of 52. How many electrons are in an uncharged atom of chromium?

A
0
B
24
C
28
D
52
14

The atomic number of beryllium (Be) is 4, and the atomic number of barium (Ba) is 56. Which comparison is best supported by this information?

A
They are in the same group because they have similar atomic masses, but they are in different periods because they have different chemical properties.
B
They are in the same group because they have similar chemical properties, but they are in different periods because they have very different atomic numbers.
C
They are in the same group because their atomic numbers are each multiples of four, but they are in different periods because they have different chemical properties.
D
They are in the same group because they have similar atomic masses, but they are in different periods because they have very different atomic numbers.
15

Isra is analyzing the properties of several samples of elements to find out which sample is a metalloid. Which set of properties most likely belongs only to a metalloid?

A
forms basic compounds and is a solid
B
has a high luster and is very brittle
C
is a gas and has low electrical conductivity
D
is brittle and forms acidic compounds

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