WorksheetsFormation of Light Elements
Total questions: 45
Worksheet time: 23mins
During Big Bang Nucleosynthesis, what formed from protons and neutrons within the first minutes after the Big Bang?
First atomic nuclei of light elements
Heavy stellar cores and iron nuclei
Molecular clouds and complex organics
Dark matter halos and black holes
Which statement best describes hydrogen (¹H) produced during primordial nucleosynthesis?
Least common element and highly reactive
Complex isotope containing two neutrons
Forms a minor component of galaxies today
Simplest element; most matter remained as protons
Deuterium (²H) is characterized by which property?
Helium isotope with two neutrons
Heavy hydrogen with one proton and one neutron
Lithium nucleus formed by beryllium decay
Light isotope with two protons
Which pair correctly matches isotope and key feature from primordial nucleosynthesis?
Deuterium: intermediate in forming helium nuclei
Lithium-7: produced in large quantities
Helium-4: most stable helium isotope
Helium-3: two protons, one neutron
Approximately what fraction of the universe’s mass after BBN is in helium-4 (⁴He)?
Nearly all remaining mass
About five percent of total mass
About twenty-five percent of mass
About half of all cosmic mass
Which statement about lithium-7 (⁷Li) from primordial nucleosynthesis is accurate?
Formed exclusively inside massive stars
Contains two protons and one neutron
Dominant product accounting for most cosmic mass
Produced in trace amounts; some from beryllium-7 decay
Choose all correct consequences of light-element formation for later cosmic evolution.
Eliminated need for stellar nucleosynthesis
Provided foundation for later chemical evolution
Instantly created complex molecules like CO₂
Enabled formation of heavier elements inside stars
What observation led Hubble to conclude the universe is expanding?
Stars inside galaxies change color rapidly
All galaxies appear blue and approach
Most galaxies show redshift and recede
Galaxies orbit each other randomly
Which statement about redshift in cosmology is correct?
It only affects nearby stars within the Milky Way
It occurs because light sources cool down
It arises as space stretches, carrying galaxies apart
It results from Earth’s rotation changing wavelengths
Select all true relationships captured by Hubble’s Law regarding galaxy recession.
Recession speed increases with distance
Farther galaxies recede more slowly
Space contraction causes blue-shift in distant galaxies
Greater redshift corresponds to faster recession
In the context of BBN, which sequence properly links particles to nuclei formation?
Photons collapse into hydrogen atoms
Protons and neutrons combine to form first nuclei
Electrons fuse into helium nuclei
Neutrinos assemble into lithium isotopes
Which pair of isotopes correctly identifies their composition from primordial nucleosynthesis?
Helium-4: two protons, two neutrons
Deuterium: one proton, one neutron
Hydrogen-1: one proton, one neutron
Helium-3: two protons, one neutron
Which physical process made the universe transparent, allowing photons to travel freely and form the Cosmic Microwave Background?
Cooling below 100 Kelvin enabling scattering
Decay of dark matter into low-energy photons
Recombination of electrons with protons into hydrogen
Ionization of neutral atoms by hot plasma
Before recombination, why couldn’t light propagate freely through the early universe?
Photons were redshifted beyond detectable wavelengths
Photons were absorbed by neutral hydrogen atoms
Photons were constantly scattered by charged particles
Photons were trapped by strong magnetic fields
Who detected the CMB in 1965 and what instrument did they use?
Hubble and Humason using optical telescope
Planck team using microwave spectrometer
Penzias and Wilson using radio antenna
Gamow and Alpher using particle accelerator
What feature of the detected signal convinced researchers it was relic radiation from the Big Bang?
It was confined to a narrow radio frequency band
It showed optical absorption lines of hydrogen
It varied strongly with direction and time
It matched predictions and was uniform in all directions
Which Nobel Prize recognition is associated with the discovery of the CMB?
2006 Nobel Prize in Astronomy
1993 Nobel Prize in Physics
1965 Nobel Prize in Chemistry
1978 Nobel Prize in Physics
The term anisotropies in the CMB refers to which property?
Random noise from radio instruments
Tiny directional temperature fluctuations
Large-scale density voids and filaments
Uniform microwave emission everywhere
What cosmological significance do CMB anisotropies have?
They represent late-time galaxy mergers
They represent early density differences
They represent cosmic-ray background
They represent solar system interference
Match each mission with its primary CMB contribution.
WMAP: full-sky temperature maps, age and composition
Planck: most precise data, age 13.8 billion years
COBE: first anisotropy detection, blackbody spectrum
Which set best describes what CMB data revealed about the universe’s composition?
~5% normal matter, ~27% dark matter, ~68% dark energy
~95% normal matter, ~3% dark matter, ~2% dark energy
~50% normal matter, ~30% dark matter, ~20% dark energy
~10% normal matter, ~45% dark matter, ~45% dark energy
What large-scale geometric property of the universe is inferred from the CMB?
The universe is negatively curved
The universe is spatially flat
The universe is positively curved
The universe is fractal at all scales
Which aspects of cosmology can be tested using the CMB? Select all that apply.
Cosmic inflation scenarios
Planetary formation mechanisms
Dark matter properties
Dark energy behavior
Why is the CMB considered a “baby picture” of the universe?
It records the first stars’ spectra
It images galaxies forming today
It shows the universe at 13.8 billion years old
It depicts conditions ~380,000 years after the Big Bang
How does the CMB help determine the Hubble constant?
By measuring galaxy rotation curves directly
By fitting anisotropy patterns to expansion models
By timing pulsars in distant clusters
By comparing solar abundances to microwave flux
Which statement best describes the CMB today?
It exists only near galaxies due to local heating
It has warmed as the universe contracts
It still fills space and is detectable by radio telescopes
It no longer fills space as expansion diluted it
Which statement best captures the connection between CMB uniformity and structure formation?
Perfect uniformity prevented any structure formation
Tiny non-uniformities seeded later galaxies and stars
Large anisotropies immediately created black holes
Uniform regions collapsed while hot spots expanded
At roughly 1 second after the Big Bang, what major event occurred at a temperature near 1010K ?
Fusion fully stopped
Protons and neutrons formed
Neutrinos decoupled
Light nuclei formed
When does nuclear fusion effectively cease because the universe cools too much for reactions?
From ~20 minutes onward
Between 3–20 minutes
At 3 seconds
At 1 second
Which reaction creates deuterium during BBN?
3He + 4He → 7Be → 7Li
3He + n → 4He + γ
2H + p → 3He + γ
p + n → 2H + γ
Which two reactions directly produce helium isotopes with gamma emission?
p + n → 2H + γ
2H + p → 3He + γ
3He + n → 4He + γ
3He + 4He → 7Be → 7Li
Which pathway leads to lithium-7 during primordial nucleosynthesis?
2H + p → 3He + γ
3He + n → 4He + γ
3He + 4He → 7Be → 7Li
p + n → 2H + γ
Which statement best describes neutrino decoupling in the BBN timeline?
It occurs after CMB emission appears
It occurs near 3 seconds and freezes n/p ratio
It occurs at 1 second and forms protons
It occurs at 20 minutes and stops fusion
Which element is the most abundant by mass after BBN?
Hydrogen (~75%)
Helium-4 (~25%)
Lithium-7 (very small)
Deuterium (~0.01%)
Why is deuterium considered a sensitive probe of early-universe conditions?
It is the second most abundant element
It is easily destroyed in stars
It forms only at low densities
Its abundance responds to baryon density
Which isotopes are noted as light nuclei formed during BBN?
3He
4He
7Li
2H (deuterium)
Which statement summarizes the lithium problem in cosmology?
Predicted lithium exceeds helium-4
Observed lithium is lower than predicted
Lithium abundance is ~25% by mass
Lithium forms only after CMB era
What fraction of the universe’s energy is ordinary (baryonic) matter as inferred from BBN element ratios?
About 1–2%
About 4–5%
About 50–60%
About 20–25%
How are BBN and the CMB temporally related?
Both occurred simultaneously within hours
CMB occurred first; BBN happened millions of years later
BBN followed the CMB by several centuries
BBN occurred minutes; CMB appeared ~380,000 years later
Which discovery demonstrated the universe is expanding and supports the Big Bang model?
Solar neutrino measurements
CMB detection
Hubble’s observation
Quasar redshift periodicity
Which pair together gives a consistent picture of the universe’s composition, age, and early conditions?
Planetary nebulae and supernovae
Galactic rotation curves and pulsars
BBN element ratios and the CMB
Solar spectra and lunar samples
Which set lists the first light elements formed by primordial nucleosynthesis?
Deuterium (D)
Hydrogen (H)
Lithium (Li)
Helium (He)
Which isotope is described as a light, stable helium isotope with trace abundance after BBN?
7Li
4He
3He
2H
Which timeline temperature is associated with the formation of protons and neutrons?
108 K
~5×10^9 K
~ 109 K
~ 1010 K
Which process provides the raw hydrogen and helium that later fuel star formation?
Planetary nebula ejection
Stellar core collapse
Galactic chemical recycling
Primordial nucleosynthesis
