name:
9. the half - life of an isotope is the time required for half the nuclei in a sample to
a. undergo radioactive decay.
c. undergo nuclear fusion.
b. react chemically.
d. undergo nuclear fission.
10. which of the following defines one atomic mass unit?
a. one - twelfth the mass of one carbon - 12 atom
b. the mass of one electron
c. the mass of the nucleus of an isotope
d. the total mass of one carbon - 12 atom
11. an isotope has 19 protons and 36 neutrons. its nuclear notation is
a. ( _{19}^{35}k )
c. ( _{19}^{55}k )
b. ( _{36}^{55}kr )
d. ( _{36}^{19}kr )
12. which statement about nuclear reactions is not true?
a. energy in the sun is produced by nuclear fusion reactions.
b. control rods in nuclear reactors help prevent dangerous chain reactions.
c. in fission, nuclei are split, and in fusion, nuclei are combined.
d. the main desired product of nuclear power plants is the daughter nuclei of uranium.
13. during radioactive decay, the nucleus breaks up into
a. less stable nucleus with more mass
c. more stable nucleus with more mass.
b. less stable nucleus with less mass
d. more stable nucleus with less mass.
14. which of the following is true about subatomic particles?
a. protons are positively charged and the lightest subatomic particle.
b. electrons are negatively charged and are the heaviest subatomic particle.
c. the mass of a neutron nearly equals the mass of a proton.
d. neutrons have no charge and are the lightest subatomic particle.
15. which of the following statements is not true?
a. the nucleus of an atom has a net (sum total) positive charge.
b. atoms of the same element can have different mass numbers.
c. isotopes of an element have different numbers of protons.
d. atoms are mostly empty space.
16. an element is automatically radioactive if its atomic number is
a. greater than 82
c. greater than 56
b. less than 82
d. less than 56
17. an atom is considered \electrically neutral\ when
a. the numbers of protons and neutrons are the same.
b. neutrons balance the protons and electrons.
c. the numbers of protons and electrons are the same.
d. nuclear forces stabilize the charges.

Question

name:
9. the half - life of an isotope is the time required for half the nuclei in a sample to
 a. undergo radioactive decay.
 c. undergo nuclear fusion.
 b. react chemically.
 d. undergo nuclear fission.
10. which of the following defines one atomic mass unit?
 a. one - twelfth the mass of one carbon - 12 atom
 b. the mass of one electron
 c. the mass of the nucleus of an isotope
 d. the total mass of one carbon - 12 atom
11. an isotope has 19 protons and 36 neutrons. its nuclear notation is
 a. ( _{19}^{35}k )
 c. ( _{19}^{55}k )
 b. ( _{36}^{55}kr )
 d. ( _{36}^{19}kr )
12. which statement about nuclear reactions is not true?
 a. energy in the sun is produced by nuclear fusion reactions.
 b. control rods in nuclear reactors help prevent dangerous chain reactions.
 c. in fission, nuclei are split, and in fusion, nuclei are combined.
 d. the main desired product of nuclear power plants is the daughter nuclei of uranium.
13. during radioactive decay, the nucleus breaks up into
 a. less stable nucleus with more mass
 c. more stable nucleus with more mass.
 b. less stable nucleus with less mass
 d. more stable nucleus with less mass.
14. which of the following is true about subatomic particles?
 a. protons are positively charged and the lightest subatomic particle.
 b. electrons are negatively charged and are the heaviest subatomic particle.
 c. the mass of a neutron nearly equals the mass of a proton.
 d. neutrons have no charge and are the lightest subatomic particle.
15. which of the following statements is not true?
 a. the nucleus of an atom has a net (sum total) positive charge.
 b. atoms of the same element can have different mass numbers.
 c. isotopes of an element have different numbers of protons.
 d. atoms are mostly empty space.
16. an element is automatically radioactive if its atomic number is
 a. greater than 82
 c. greater than 56
 b. less than 82
 d. less than 56
17. an atom is considered \electrically neutral\ when
 a. the numbers of protons and neutrons are the same.
 b. neutrons balance the protons and electrons.
 c. the numbers of protons and electrons are the same.
 d. nuclear forces stabilize the charges.

Accepted Answer

### 9.
# Brief Explanations:
The half - life is defined for radioactive decay. Nuclear fusion and fission are different nuclear processes. Chemical reactions involve electrons, not nuclei.
# Answer:
a. undergo radioactive decay

### 10.
# Brief Explanations:
One atomic mass unit (amu) is defined as one - twelfth of the mass of a carbon - 12 atom.
# Answer:
a. one - twelfth the mass of one carbon - 12 atom

### 11.
# Brief Explanations:
The atomic number $Z$ (number of protons) for potassium ($K$) is $19$. The mass number $A=Z + N=19 + 36=55$. The nuclear notation is $_{Z}^{A}X$, so it is $_{19}^{55}K$
# Answer:
a. $_{19}^{55}K$

### 12.
# Brief Explanations:
In nuclear power plants, the main desired product is energy, not the daughter nuclei of Uranium.
# Answer:
d. The main desired product of nuclear power plants is the daughter nuclei of Uranium.

### 13.
# Brief Explanations:
During radioactive decay, a nucleus breaks up into a more stable nucleus. Since energy is released (mass - energy equivalence $E = mc^{2}$), the more stable nucleus has less mass.
# Answer:
d. more stable nucleus with less mass.

### 14.
# Brief Explanations:
Protons have a mass of approximately $1.67\times10^{- 27}\text{kg}$, neutrons have a mass of approximately $1.68\times10^{-27}\text{kg}$, electrons have a mass of approximately $9.11\times 10^{-31}\text{kg}$. Protons are positively charged, electrons are negatively charged, and neutrons are neutral.
# Answer:
c. The mass of a neutron nearly equals the mass of a proton.

### 15.
# Brief Explanations:
Isotopes of an element have the same number of protons (same atomic number).
# Answer:
c. Isotopes of an element have different numbers of protons.

### 16.
# Brief Explanations:
Elements with atomic number greater than $82$ (lead) are automatically radioactive.
# Answer:
a. greater than $82$

### 17.
# Brief Explanations:
An atom is electrically neutral when the number of protons (positive charge) equals the number of electrons (negative charge).
# Answer:
c. the numbers of protons and electrons are the same.

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Question

Explanation:

9.

Answer:

10.