NLN NEX - Science Questions / 90 Quizzes with Certified Solution/ 2024-
2025.
Compare and contrast nuclear fission and nuclear fusion - (answers)Nuclear Fission: Splitting of
a nucleus into smaller particles
Nuclear Fusion: Joining of nuclei to form a heavier nucleus.
Define stable and radioactive isotopes - (answers)Stable Isotopes: Not observed to decay, non-
radioactive.
Radioactive Isotopes: Unstable nuclei can undergo spontaneous nuclear reactions. Cannot be
predicted when nucleus will decay.
Explain the relative bond length and bond strength of single, double, and triple covalent bonds. -
(answers)Bond length of covalent bond is the distance between the nuclei of two covalently
bonded atoms.
Single bonds: between one pair of electrons, and are the weakest. longest of the three bond types.
Double Bonds: between two pairs of electrons. stronger than single bonds, shorter than single
bonds.
Triple Bonds: between three pairs of electrons. stronger than double bonds, shortest bond length.
Describe Ionic bonding and give an example - (answers)Ionic bonding: Transfer of electrons
between atoms.
Cation: Positive ion formed losing one or more electrons
Anion: Negative ion formed gaining one or more electrons.
Distinguish between polar covalent bonds, nonpolar covalent bonds, and hybridization. -
(answers)Polar covalent Bonds: electrons are shared unequally between atoms
Nonpolar covalent Bonds: Electrons are shared equally between atoms.
Hybridization: Mixing of atomic orbitals on same atom to form new hybrid orbitals.
,Describe Gold foil Experiment and its significance. - (answers)Disproved the plum pudding
experiment. Gold foil experiment led to the discovery of the nucleus of an atom. Rutherford's lab
bombarded a thin gold foil with high=speed helium ions. some of the ions were reflected by the
foil. Concluded that the atom has a hard central core (nucleus).
Describe the two categories of pure substances - (answers)Elements: consists of one type of
atom. Can be monatomic, diatomic, or polyatomic.
Compounds: Consists of more than one type of atom.
Describe a suspension and provide an example. - (answers)Heterogeneous mixture in which
particle size of substance is too large to be kept in suspension by Brownian motion.
Example: Sand stirred into water, after a while water will form a layer on top of the sand.
Contrast chemical and physical changes in list examples of each. - (answers)Physical Change:
Do not produce new substances. Atoms can be rearranged. Melting, freezing. Ice, boiling of
water, sugar dissolving into water, and crushing a piece of chalk into a fine powder.
Contrast chemical and physical properties and list examples of each. - (answers)Physical: Can be
seen or observed without changing the identity or composition of matter. Mass, Volume, Density,
Color, Freezing point, Oder.
Chemical: Cannot be measured without changing the identity or composition of matter.
Flammability, oxidation, corrosivity, reactivity.
Explain how the cathode ray tube (CRT) was used in the discovery of the electron. -
(answers)Electrons were discovered by Joseph John Thomson through scientific work with
cathode ray tubes (CRTs). Thomson showed that cathode rays were negatively charged particles.
Could not determine charge or mass of electrons, but could determine ratio of the charge to the
mass.
Discuss past atomic models and theories - (answers)Democritus 400 B.C.: Concept of atom
John Dalton: Billiard ball model, solid sphere.
J.J. Thomson: Plum pudding & Raisin bun model.
Ernest Rutherford: Planetary & Nuclear model.
,Niels Bohr: Bohr model.
Louis de Broglie & Erwin Schrodinger: Electron cloud & quantum mechanical model.
List and describe the three major subatomic particles. - (answers)Proton: In nucleus, charge of +1
Neutron: In nucleus, charge of 0
Electron: Outside of nucleus, charge of -1
Discuss Rutherford scattering. - (answers)Rutherford Scattering: Elastic scattering of charged
particles by the coulomb interaction.
Conclusion: Most space inside atom is empty because most of the α-particles passed through the
gold foil without getting deflected.
Answer the following questions about Isotopes:
1. What is the definition of an isotope?
2. How are isotopes represented using their name and mass?
3. How are isotopes represented using their symbol, mass number, and atomic number? -
(answers)1. Same element with different # nucleus.
2. Written as: (ex.) Carbon-12, Carbon-13
3. Shown as: 12/6C & 13/6C
top # (12) representing mass #
bottom# (6) representing atomic #
C representing element symbol
List and describe the four quantum numbers. - (answers)1. Principal Quantum # (n): Energy level
of electron representing average distance from nucleus.
2. Azimuthal Quantum # (l): shape of orbital, related to subshell (s, p, f, d)
3. Magnetic Quantum # (m1): Orientation of orbital in space
4. Spin Quantum # (ms): Represents the spin of electron either +1/2 or -1/2
Discuss the basic organization of matter. - (answers)Matter:
, Can it be physically separated?
YES-->MIXTURE
NO-->PURE SUBSTANCE
If YES, Is composition uniform?
YES--> HOMOGENOUS MIXTURE (SOLUTION)
NO--> HETEROGENEOUS MIXTURE
colloids or suspensions
IF NO, Can it be chemically decomposed?
YES-->COMPOUND
NO-->ELEMENT
Distinguish between atomic number and mass number - (answers)Atomic #: Only counts
protons, determines element
Mass#: Counts both protons & neutrons
Atomic # 8
Element Symbol O
Atomic Mass (amu) 15.999
Define average atomic mass, and state the appropriate unit. Explain how the average atomic
mass is obtained for an element. - (answers)AAM: weighted average of the masses of all the
naturally occurring isotopes of an atom in comparison to the carbon-12 isotope.
AAM of copper is 63 amu because of 29 protons and 34 electrons.
Contrast intensive and extensive properties and list examples of each. - (answers)Intensive
Properties: Does not change when more or less is added or taken.
Red paint + red paint = red paint
2025.
Compare and contrast nuclear fission and nuclear fusion - (answers)Nuclear Fission: Splitting of
a nucleus into smaller particles
Nuclear Fusion: Joining of nuclei to form a heavier nucleus.
Define stable and radioactive isotopes - (answers)Stable Isotopes: Not observed to decay, non-
radioactive.
Radioactive Isotopes: Unstable nuclei can undergo spontaneous nuclear reactions. Cannot be
predicted when nucleus will decay.
Explain the relative bond length and bond strength of single, double, and triple covalent bonds. -
(answers)Bond length of covalent bond is the distance between the nuclei of two covalently
bonded atoms.
Single bonds: between one pair of electrons, and are the weakest. longest of the three bond types.
Double Bonds: between two pairs of electrons. stronger than single bonds, shorter than single
bonds.
Triple Bonds: between three pairs of electrons. stronger than double bonds, shortest bond length.
Describe Ionic bonding and give an example - (answers)Ionic bonding: Transfer of electrons
between atoms.
Cation: Positive ion formed losing one or more electrons
Anion: Negative ion formed gaining one or more electrons.
Distinguish between polar covalent bonds, nonpolar covalent bonds, and hybridization. -
(answers)Polar covalent Bonds: electrons are shared unequally between atoms
Nonpolar covalent Bonds: Electrons are shared equally between atoms.
Hybridization: Mixing of atomic orbitals on same atom to form new hybrid orbitals.
,Describe Gold foil Experiment and its significance. - (answers)Disproved the plum pudding
experiment. Gold foil experiment led to the discovery of the nucleus of an atom. Rutherford's lab
bombarded a thin gold foil with high=speed helium ions. some of the ions were reflected by the
foil. Concluded that the atom has a hard central core (nucleus).
Describe the two categories of pure substances - (answers)Elements: consists of one type of
atom. Can be monatomic, diatomic, or polyatomic.
Compounds: Consists of more than one type of atom.
Describe a suspension and provide an example. - (answers)Heterogeneous mixture in which
particle size of substance is too large to be kept in suspension by Brownian motion.
Example: Sand stirred into water, after a while water will form a layer on top of the sand.
Contrast chemical and physical changes in list examples of each. - (answers)Physical Change:
Do not produce new substances. Atoms can be rearranged. Melting, freezing. Ice, boiling of
water, sugar dissolving into water, and crushing a piece of chalk into a fine powder.
Contrast chemical and physical properties and list examples of each. - (answers)Physical: Can be
seen or observed without changing the identity or composition of matter. Mass, Volume, Density,
Color, Freezing point, Oder.
Chemical: Cannot be measured without changing the identity or composition of matter.
Flammability, oxidation, corrosivity, reactivity.
Explain how the cathode ray tube (CRT) was used in the discovery of the electron. -
(answers)Electrons were discovered by Joseph John Thomson through scientific work with
cathode ray tubes (CRTs). Thomson showed that cathode rays were negatively charged particles.
Could not determine charge or mass of electrons, but could determine ratio of the charge to the
mass.
Discuss past atomic models and theories - (answers)Democritus 400 B.C.: Concept of atom
John Dalton: Billiard ball model, solid sphere.
J.J. Thomson: Plum pudding & Raisin bun model.
Ernest Rutherford: Planetary & Nuclear model.
,Niels Bohr: Bohr model.
Louis de Broglie & Erwin Schrodinger: Electron cloud & quantum mechanical model.
List and describe the three major subatomic particles. - (answers)Proton: In nucleus, charge of +1
Neutron: In nucleus, charge of 0
Electron: Outside of nucleus, charge of -1
Discuss Rutherford scattering. - (answers)Rutherford Scattering: Elastic scattering of charged
particles by the coulomb interaction.
Conclusion: Most space inside atom is empty because most of the α-particles passed through the
gold foil without getting deflected.
Answer the following questions about Isotopes:
1. What is the definition of an isotope?
2. How are isotopes represented using their name and mass?
3. How are isotopes represented using their symbol, mass number, and atomic number? -
(answers)1. Same element with different # nucleus.
2. Written as: (ex.) Carbon-12, Carbon-13
3. Shown as: 12/6C & 13/6C
top # (12) representing mass #
bottom# (6) representing atomic #
C representing element symbol
List and describe the four quantum numbers. - (answers)1. Principal Quantum # (n): Energy level
of electron representing average distance from nucleus.
2. Azimuthal Quantum # (l): shape of orbital, related to subshell (s, p, f, d)
3. Magnetic Quantum # (m1): Orientation of orbital in space
4. Spin Quantum # (ms): Represents the spin of electron either +1/2 or -1/2
Discuss the basic organization of matter. - (answers)Matter:
, Can it be physically separated?
YES-->MIXTURE
NO-->PURE SUBSTANCE
If YES, Is composition uniform?
YES--> HOMOGENOUS MIXTURE (SOLUTION)
NO--> HETEROGENEOUS MIXTURE
colloids or suspensions
IF NO, Can it be chemically decomposed?
YES-->COMPOUND
NO-->ELEMENT
Distinguish between atomic number and mass number - (answers)Atomic #: Only counts
protons, determines element
Mass#: Counts both protons & neutrons
Atomic # 8
Element Symbol O
Atomic Mass (amu) 15.999
Define average atomic mass, and state the appropriate unit. Explain how the average atomic
mass is obtained for an element. - (answers)AAM: weighted average of the masses of all the
naturally occurring isotopes of an atom in comparison to the carbon-12 isotope.
AAM of copper is 63 amu because of 29 protons and 34 electrons.
Contrast intensive and extensive properties and list examples of each. - (answers)Intensive
Properties: Does not change when more or less is added or taken.
Red paint + red paint = red paint
