18. the smallest particle of an element that retains the properties of that element is a(n) _.a. protonb. neutrong. electrond. atom19. all radioactive elements undergoc. chemical decomposition.a. fusion reactionsb. fission reactionsd. radioactive decay.20. lead has 4 stable isotopes: lead-204, lead-206, lead-207 and lead-208. which isotope is the mostabundant?a. lead-204c. lead-207b. lead-208d. lead-20621. which if the following statement is falsea. carbon-12 and carbon-13 have the same number of protonsb. elements with 83 or more protons are always radioactivec. carbon-14 and nitrogen-14 are isotopes of each otherd. the element identity is defined by the number of protons22. what does the 235 in uranium-235 represent?c. the mass defecta. the atomic numberd. the neutron numberb. the mass number23. phosphorus-32 has a half-life of 14.3 days. how many milligrams of phosphorus-32remain after 62.1 days if you start with 5.00 mg of the isotope?c. 0.0494 mga. 0.575 mgd. 0.247 mgb. 4.26 mg24. which of the following sets of symbols represents isotopes of the same element?a. 8438x 8638x 8738xb. 9142j 9242j 9340jc. 5019z 5020z 5021zd. 13859q 13355q 13354q25. select which statment is true about mass and volume of the nucleus in the atom:a. the nucleus has 99% of the volume of the atom and holds 99% of the atoms mass.b. the nucleus has 1% of the volume of the atom and holds 1% of the atoms mass.c. the nucleus has 99% of the volume of the atom and holds 1% of the atoms mass.d. the nucleus has 1% of the volume of the atom and holds 99% of the atoms mass.

Question

Accepted Answer

# 18.
## Brief Explanations:
An atom is the smallest particle of an element that retains the properties of that element. Protons, neutrons, and electrons are sub - atomic particles that make up an atom. Protons and neutrons are in the nucleus, and electrons orbit around the nucleus. But it is the atom as a whole that represents the element.
# Answer:
d. atom

# 19.
## Brief Explanations:
Radioactive elements have unstable nuclei. They undergo radioactive decay, which is the process of emitting radiation (alpha, beta, gamma) to become more stable. Fusion reactions occur in stars (combining light nuclei), fission reactions are used in nuclear power plants (splitting heavy nuclei), and chemical decomposition is a chemical change (not a nuclear property of radioactive elements).
# Answer:
d. radioactive decay

# 20.
## Brief Explanations:
Lead - 208 is the most abundant isotope of lead among the given options. This is a factual knowledge based on the isotopic abundance data of lead.
# Answer:
b. Lead - 208

# 21.
## Brief Explanations:
- Option a: Carbon - 12 and carbon - 13 are isotopes (same element, same number of protons).
- Option b: Elements with $Z\geq83$ (atomic number) are radioactive.
- Option c: Isotopes are of the same element. Carbon - 14 ($C$, $Z = 6$) and nitrogen - 14 ($N$, $Z=7$) are different elements, so they are not isotopes.
- Option d: The number of protons (atomic number) defines the element.
# Answer:
c. carbon - 14 and nitrogen - 14 are isotopes of each other

# 22.
## Brief Explanations:
In the notation $^{A}_{Z}X$ (where $X$ is the element symbol, $Z$ is the atomic number, and $A$ is the mass number), for Uranium - 235 ($^{235}_{92}U$), 235 represents the mass number ($A$). The atomic number ($Z$) for U is 92.
# Answer:
b. the mass number

# 23.
## Step - by - Step Format:
### Explanation:
## Step 1: Calculate the number of half - lives ($n$)
The formula for the number of half - lives is $n=\frac{t}{t_{1/2}}$, where $t$ is the time elapsed and $t_{1/2}$ is the half - life.
Given $t = 62.1$ days and $t_{1/2}=14.3$ days.
$n=\frac{62.1}{14.3}=4.34266\approx4$ (using whole number for simplicity in the basic decay formula $N = N_{0}(\frac{1}{2})^{n}$)
## Step 2: Use the radioactive decay formula $N = N_{0}(\frac{1}{2})^{n}$
Given $N_{0}=5.00$ mg and $n = 4$
$N=5.00\times(\frac{1}{2})^{4}$
$N = 5.00\times\frac{1}{16}$
$N=0.3125$ mg (if we use the more accurate $n = 4.34266$, $N = N_{0}e^{-\lambda t}$, where $\lambda=\frac{\ln2}{t_{1/2}}$, $\lambda=\frac{\ln2}{14.3}\approx0.0485$ per day, $N = 5e^{-0.0485\times62.1}\approx0.247$ mg)
# Answer:
d. $0.247$ mg

# 24.
## Brief Explanations:
Isotopes are of the same element, which means they have the same atomic number ($Z$). In option a, the atomic number ($Z = 38$) is the same for all three species ($^{84}_{38}X$, $^{86}_{38}X$, $^{87}_{38}X$), so they are isotopes. In option b, the third species has $Z = 40$ (different from $Z = 42$ of the first two). In option c, $Z$ values are different ($19$, $20$, $21$). In option d, $Z$ values ($59$, $55$, $54$) are different.
# Answer:
a. $^{84}_{38}X$, $^{86}_{38}X$, $^{87}_{38}X$

# 25.
## Brief Explanations:
The nucleus is a very dense part of the atom. It has about $1\%$ of the volume of the atom but holds about $99\%$ of the atom's mass. Electrons, which have very little mass ($m_{e}\ll m_{p},m_{n}$), occupy most of the volume of the atom.
# Answer:
d. The nucleus has $1\%$ of the volume of the atom and holds $99\%$ of the atom’s mass.

Sovi.AI - AI Math Tutor

QUESTION IMAGE

Question

Explanation:

18.

Answer:

19.