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NLN NEX Science study materials
NLN NEX Science study resources

NLN NEX Science practice questions

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Question 1Life and Physical Sciences (biology, chemistry, physics)

Which organelle is the main site of ATP production in a eukaryotic cell?

  1. Golgi apparatus
  2. Lysosome
  3. Mitochondrion Correct answer.
  4. Ribosome

Explanation

Mitochondria carry out aerobic respiration, using the electron transport chain to build most of the cell's ATP supply. Ribosomes assemble proteins, the Golgi modifies and packages them, and lysosomes handle digestion.

Question 2Life and Physical Sciences (biology, chemistry, physics)

In photosynthesis, plants combine carbon dioxide and water using light energy to make glucose and release which gas?

  1. Oxygen Correct answer.
  2. Hydrogen
  3. Methane
  4. Nitrogen

Explanation

The light reactions split water molecules, producing oxygen as a byproduct while generating ATP and NADPH for the Calvin cycle. The carbon from carbon dioxide is then fixed into glucose.

Question 3Life and Physical Sciences (biology, chemistry, physics)

Which statement best describes the particles in a solid?

  1. They move freely past one another and expand to fill the container.
  2. They are widely separated and move rapidly in all directions.
  3. They are randomly arranged and have no definite volume.
  4. They vibrate around fixed positions and remain close together. Correct answer.

Explanation

In a solid, intermolecular forces hold particles in a lattice, so they can only vibrate about fixed positions. This fixed arrangement gives solids a definite shape and volume.

Question 4Life and Physical Sciences (biology, chemistry, physics)

The atomic number of an element is equal to the number of

  1. neutrons in the nucleus
  2. electrons in the outermost shell
  3. protons in the nucleus Correct answer.
  4. protons plus neutrons in the nucleus

Explanation

Atomic number counts protons, which uniquely identify the element and determine its position on the periodic table. Neutrons plus protons give the mass number, and outer-shell electrons vary with bonding state.

Question 5Life and Physical Sciences (biology, chemistry, physics)

A book resting on a desk stays at rest until someone pushes it. This statement illustrates which principle?

  1. Newton's third law
  2. Law of universal gravitation
  3. Newton's second law
  4. Newton's first law Correct answer.

Explanation

Newton's first law states that an object remains at rest or in uniform motion unless a net external force acts on it. This property is called inertia.

Question 6Life and Physical Sciences (biology, chemistry, physics)

Which pH value indicates a neutral solution at room temperature?

  1. 7 Correct answer.
  2. 2
  3. 9
  4. 12

Explanation

The pH scale runs from 0 to 14, with 7 marking the point where hydrogen ion and hydroxide ion concentrations are equal. Values below 7 are acidic and values above 7 are basic.

Question 7Life and Physical Sciences (biology, chemistry, physics)

Which blood component is mainly responsible for carrying oxygen from the lungs to body tissues?

  1. White blood cells
  2. Red blood cells Correct answer.
  3. Platelets
  4. Plasma proteins

Explanation

Red blood cells are packed with hemoglobin, an iron-containing protein that binds oxygen in the lungs and releases it in tissues. This makes them the principal oxygen carriers of blood.

Question 8Life and Physical Sciences (biology, chemistry, physics)

Which energy source is classified as renewable?

  1. Petroleum
  2. Wind Correct answer.
  3. Coal
  4. Natural gas

Explanation

Wind is replenished continuously by solar heating of the atmosphere, so it is not depleted by use. Coal, petroleum, and natural gas are fossil fuels formed over millions of years and are consumed faster than they form.

Question 9Life and Physical Sciences (biology, chemistry, physics)

A plant cell is placed in a hypotonic solution. What is the expected result?

  1. Solutes leave the cell until concentrations equalize.
  2. There is no net water movement because the solutions are isotonic.
  3. Water enters the cell and the cell becomes turgid. Correct answer.
  4. Water leaves the cell and the cell shrinks.

Explanation

In a hypotonic solution the solute concentration outside the cell is lower than inside, so water moves inward by osmosis. The rigid cell wall resists expansion and the cell becomes firm, or turgid.

Question 10Life and Physical Sciences (biology, chemistry, physics)

Heating an enzyme far above its optimal temperature lowers reaction rate mainly because

  1. the enzyme concentration in the cell increases
  2. the reaction switches from exothermic to endothermic
  3. the enzyme's active site changes shape Correct answer.
  4. the substrate molecules are destroyed by the heat

Explanation

Enzymes are proteins whose function depends on a precise three-dimensional active site. Excess heat breaks the bonds holding that shape, denaturing the enzyme so the substrate no longer fits.

Question 11Life and Physical Sciences (biology, chemistry, physics)

In a DNA molecule, adenine normally pairs with which base?

  1. Uracil
  2. Guanine
  3. Thymine Correct answer.
  4. Cytosine

Explanation

DNA uses complementary base pairing in which adenine pairs with thymine through two hydrogen bonds and guanine pairs with cytosine through three. This pairing allows each strand to serve as a template during replication.

Question 12Life and Physical Sciences (biology, chemistry, physics)

The cells produced at the end of meiosis are best described as

  1. diploid cells with twice the chromosome number
  2. haploid cells with half the chromosome number Correct answer.
  3. haploid cells with twice the chromosome number
  4. diploid cells genetically identical to the parent cell

Explanation

Meiosis includes two successive divisions after a single round of DNA replication, reducing the chromosome number by half. The resulting gametes are haploid and genetically distinct from the parent cell.

Question 13Life and Physical Sciences (biology, chemistry, physics)

For the balanced combustion reaction CH₄ + 2O₂ → CO₂ + 2H₂O, what is the sum of all the coefficients?

  1. 6 Correct answer.
  2. 8
  3. 5
  4. 4

Explanation

The written coefficients are 1 for CH₄, 2 for O₂, 1 for CO₂, and 2 for H₂O, which add to 6. Checking atom counts confirms the equation is balanced: one carbon, four hydrogen, and four oxygen atoms on each side.

Question 14Life and Physical Sciences (biology, chemistry, physics)

Using C = 12 g/mol and O = 16 g/mol, what is the molar mass of carbon dioxide, CO₂?

  1. 28 g/mol
  2. 48 g/mol
  3. 32 g/mol
  4. 44 g/mol Correct answer.

Explanation

Molar mass is the sum of the atomic masses of all atoms in the formula: 12 g/mol for one carbon plus 2 × 16 g/mol for two oxygens, giving 44 g/mol.

Question 15Life and Physical Sciences (biology, chemistry, physics)

Which type of bond forms when a metal transfers electrons to a nonmetal?

  1. Hydrogen bond
  2. Metallic bond
  3. Covalent bond
  4. Ionic bond Correct answer.

Explanation

Transfer of electrons from a metal atom to a nonmetal atom produces oppositely charged ions that attract each other electrostatically, forming an ionic bond. Covalent bonds instead involve sharing electrons.

Question 16Life and Physical Sciences (biology, chemistry, physics)

A 12 V battery is connected across a 4 Ω resistor. What current flows through the resistor?

  1. 48 A
  2. 0.33 A
  3. 3 A Correct answer.
  4. 16 A

Explanation

Ohm's law states that current equals voltage divided by resistance, I = V/R. Substituting gives 12 V ÷ 4 Ω = 3 A.

Question 17Life and Physical Sciences (biology, chemistry, physics)

A car travels 150 meters in 10 seconds at a constant rate. What is its average speed?

  1. 15 m/s Correct answer.
  2. 1500 m/s
  3. 150 m/s
  4. 1.5 m/s

Explanation

Average speed equals total distance divided by total time. Dividing 150 m by 10 s gives 15 m/s.

Question 18Life and Physical Sciences (biology, chemistry, physics)

A block has a mass of 60 g and a volume of 20 cm³. What is its density?

  1. 1.2 g/cm³
  2. 3 g/cm³ Correct answer.
  3. 0.33 g/cm³
  4. 120 g/cm³

Explanation

Density is mass divided by volume, so 60 g ÷ 20 cm³ = 3 g/cm³. This value means each cubic centimeter of the block has a mass of 3 grams.

Question 19Life and Physical Sciences (biology, chemistry, physics)

Which statement best describes natural selection?

  1. Organisms acquire helpful traits during their lifetime and pass them to offspring.
  2. Traits change because organisms need them in order to survive.
  3. Individuals with inherited helpful traits survive and reproduce more. Correct answer.
  4. All individuals in a population have equal reproductive success.

Explanation

Natural selection acts on heritable variation already present in a population: individuals whose inherited traits suit the environment leave more offspring, so those traits become more common over generations.

Question 20Life and Physical Sciences (biology, chemistry, physics)

Two heterozygous tall pea plants (Tt) are crossed. What fraction of the offspring is expected to be short (tt)?

  1. 0
  2. 1/4 Correct answer.
  3. 3/4
  4. 1/2

Explanation

A Tt × Tt cross yields genotypes TT, Tt, Tt, and tt in equal proportions. Only the tt combination shows the recessive short phenotype, so one quarter of the offspring are expected to be short.

Question 21Life and Physical Sciences (biology, chemistry, physics)

For the reaction 2H₂ + O₂ → 2H₂O, 4 mol of H₂ is mixed with 1 mol of O₂. Which reactant limits the reaction, and how much water forms?

  1. H₂ is limiting, and 4 mol of H₂O form.
  2. Neither is limiting, and 4 mol of H₂O form.
  3. O₂ is limiting, and 1 mol of H₂O forms.
  4. O₂ is limiting, and 2 mol of H₂O form. Correct answer.

Explanation

Four moles of H₂ would require 2 mol of O₂, but only 1 mol is available, so O₂ runs out first. The stoichiometric ratio of 1 mol O₂ to 2 mol H₂O means 2 mol of water is produced.

Question 22Life and Physical Sciences (biology, chemistry, physics)

A 5 kg object accelerates at 3 m/s² while a 25 N applied force pushes it forward. What is the magnitude of the opposing friction force?

  1. 10 N Correct answer.
  2. 5 N
  3. 15 N
  4. 40 N

Explanation

Newton's second law gives the net force as ma = 5 kg × 3 m/s² = 15 N. Since the 25 N applied force must overcome friction to leave 15 N of net force, friction equals 25 N − 15 N = 10 N.

Question 23Life and Physical Sciences (biology, chemistry, physics)

A DNA template strand reads 3′-TAC-5′. What mRNA codon is transcribed from it?

  1. ATG
  2. TAC
  3. UAC
  4. AUG Correct answer.

Explanation

Transcription builds mRNA complementary to the template strand, with uracil replacing thymine. Reading the template 3′ to 5′ gives T-A-C, so the mRNA codon is 5′-AUG-3′.

Question 24Life and Physical Sciences (biology, chemistry, physics)

Which element has the electron configuration 1s²2s²2p⁶3s²3p¹?

  1. Na
  2. Si
  3. Al Correct answer.
  4. Mg

Explanation

Adding the superscripts gives 2 + 2 + 6 + 2 + 1 = 13 electrons, and a neutral atom with 13 electrons has atomic number 13. That element is aluminum, which sits in group 13 of the periodic table.

Question 25Life and Physical Sciences (biology, chemistry, physics)

How much heat is required to raise the temperature of 200 g of water by 10 °C? (specific heat of water = 4.18 J/g·°C)

  1. 836 J
  2. 8360 J Correct answer.
  3. 4180 J
  4. 83,600 J

Explanation

The heat absorbed is calculated with q = mcΔT. Substituting gives 200 g × 4.18 J/g·°C × 10 °C = 8360 J.

Question 26Life and Physical Sciences (biology, chemistry, physics)

Which organelle is the primary site of ATP production in a eukaryotic cell?

  1. Lysosome
  2. Ribosome
  3. Mitochondrion Correct answer.
  4. Golgi apparatus

Explanation

Mitochondria house the electron transport chain and ATP synthase, which generate most of the cell's ATP through oxidative phosphorylation. Ribosomes build proteins, and the Golgi and lysosomes handle modification, packaging, and digestion rather than bulk energy production.

Question 27Life and Physical Sciences (biology, chemistry, physics)

Which gas makes up the largest share of Earth's atmosphere near sea level?

  1. Oxygen
  2. Carbon dioxide
  3. Nitrogen Correct answer.
  4. Argon

Explanation

Dry air is roughly 78% nitrogen and 21% oxygen by volume, so nitrogen is the dominant component. Carbon dioxide and argon are present only in trace amounts.

Question 28Life and Physical Sciences (biology, chemistry, physics)

Which subatomic particle carries a negative electric charge?

  1. Neutron
  2. Proton
  3. Electron Correct answer.
  4. Alpha particle

Explanation

Electrons carry a charge of -1 elementary unit and occupy the region around the nucleus. Protons are positive, and neutrons and alpha particles carry no net negative charge.

Question 29Life and Physical Sciences (biology, chemistry, physics)

Which SI unit is used to measure force?

  1. Joule
  2. Pascal
  3. Watt
  4. Newton Correct answer.

Explanation

Force is measured in newtons, where one newton is the force needed to accelerate a 1 kg mass at 1 m/s². Joules measure energy, watts measure power, and pascals measure pressure.

Question 30Life and Physical Sciences (biology, chemistry, physics)

Which molecule serves as the main direct energy currency for cellular work?

  1. Glucose
  2. Pyruvate
  3. NADH
  4. ATP Correct answer.

Explanation

ATP couples exergonic reactions to endergonic ones by transferring a phosphate group, releasing usable energy. Glucose and pyruvate are fuels that must be broken down to produce ATP, and NADH is an electron carrier rather than a direct energy currency.

Question 31Life and Physical Sciences (biology, chemistry, physics)

Which state of matter has a definite volume but takes the shape of its container?

  1. Plasma
  2. Gas
  3. Solid
  4. Liquid Correct answer.

Explanation

Particles in a liquid remain close together, giving a fixed volume, but they can slide past one another, so the liquid conforms to its container. Solids keep both shape and volume, while gases and plasmas expand to fill their containers.

Question 32Life and Physical Sciences (biology, chemistry, physics)

Which simple sugar is the main carbohydrate product that plants generate during photosynthesis?

  1. Maltose
  2. Fructose
  3. Sucrose
  4. Glucose Correct answer.

Explanation

The Calvin cycle fixes carbon dioxide into glucose, which plants then use for energy or convert into storage and transport forms. Sucrose and maltose are disaccharides assembled from simpler sugars, and fructose is produced only in smaller amounts.

Question 33Life and Physical Sciences (biology, chemistry, physics)

A light ray bends as it passes at an angle from air into water. This bending is an example of

  1. Refraction Correct answer.
  2. Diffraction
  3. Absorption
  4. Reflection

Explanation

Refraction is the change in direction of a wave when it crosses into a medium with a different wave speed. Reflection would send the ray back into the air, diffraction spreads waves around obstacles, and absorption removes energy from the beam.

Question 34Life and Physical Sciences (biology, chemistry, physics)

Which process moves ions across a cell membrane from a region of low concentration to a region of high concentration using energy from ATP?

  1. Osmosis
  2. Simple diffusion
  3. Facilitated diffusion
  4. Active transport Correct answer.

Explanation

Active transport uses energy, often from ATP hydrolysis, to move solutes against their concentration gradient. Diffusion and osmosis are passive and always move material down a gradient.

Question 35Life and Physical Sciences (biology, chemistry, physics)

A person with genotype I^A I^B has blood type AB, in which both A and B antigens are fully expressed. This pattern illustrates

  1. Polygenic inheritance
  2. Incomplete dominance
  3. Codominance Correct answer.
  4. Complete dominance

Explanation

In codominance, both alleles are expressed fully and independently in the heterozygote, as with the A and B blood group antigens. Incomplete dominance would instead produce a blended intermediate trait.

Question 36Life and Physical Sciences (biology, chemistry, physics)

During which phase of the cell cycle does DNA replication take place?

  1. M phase
  2. G1 phase
  3. G2 phase
  4. S phase Correct answer.

Explanation

The S phase, or synthesis phase, is when each chromosome is copied so that the cell has two sister chromatids. G1 and G2 are growth and checkpoint phases, and M phase is when the duplicated chromosomes are separated and the cell divides.

Question 37Life and Physical Sciences (biology, chemistry, physics)

An atom of sodium-23 has an atomic number of 11. How many neutrons are in its nucleus?

  1. 12 Correct answer.
  2. 34
  3. 23
  4. 11

Explanation

The mass number equals protons plus neutrons, so neutrons = 23 - 11 = 12. The atomic number itself gives only the proton count.

Question 38Life and Physical Sciences (biology, chemistry, physics)

What is the molarity of a solution prepared by dissolving 0.50 mol of NaCl in enough water to make 2.0 L of solution?

  1. 1.0 M
  2. 0.50 M
  3. 0.25 M Correct answer.
  4. 4.0 M

Explanation

Molarity equals moles of solute divided by liters of solution: 0.50 mol / 2.0 L = 0.25 M. The volume must be the total solution volume, not the volume of water added.

Question 39Life and Physical Sciences (biology, chemistry, physics)

A sealed rigid container holds a fixed amount of gas. What happens to the gas pressure when the container is warmed?

  1. It changes unpredictably with temperature
  2. It stays constant because the volume is fixed
  3. It rises as particles hit the walls harder Correct answer.
  4. It falls steadily as the gas is warmed

Explanation

At constant volume, raising the temperature increases the average kinetic energy of the gas particles. They strike the container walls more frequently and with greater force, so the pressure rises in direct proportion to absolute temperature.

Question 40Life and Physical Sciences (biology, chemistry, physics)

When an acid reacts with a base in a neutralization reaction, which two types of products are formed?

  1. An oxide and hydrogen
  2. A salt and water Correct answer.
  3. A gas and a metal
  4. Two new acids

Explanation

Neutralization combines hydrogen ions from the acid with hydroxide ions from the base to produce water, leaving the spectator ions to form a salt. For example, HCl plus NaOH gives NaCl plus H2O.

Question 41Life and Physical Sciences (biology, chemistry, physics)

A worker pushes a crate with a constant horizontal force of 20 N over a distance of 3.0 m in the direction of the force. How much work is done on the crate?

  1. 23 J
  2. 180 J
  3. 60 J Correct answer.
  4. 6.7 J

Explanation

Work equals force times displacement in the direction of the force, so 20 N x 3.0 m = 60 J. Adding or dividing the values instead of multiplying gives an incorrect result.

Question 42Life and Physical Sciences (biology, chemistry, physics)

A hockey puck slides across smooth ice at constant velocity. Which concept best explains why it continues moving without a continuing push?

  1. Gravity
  2. Air resistance
  3. Friction
  4. Inertia Correct answer.

Explanation

Newton's first law states that an object keeps its velocity unless a net external force acts on it; this property is called inertia. Friction and air resistance are forces that would slow the puck, not sustain its motion.

Question 43Life and Physical Sciences (biology, chemistry, physics)

A wave has a frequency of 50 Hz and a wavelength of 2.0 m. What is its speed?

  1. 0.04 m/s
  2. 25 m/s
  3. 100 m/s Correct answer.
  4. 52 m/s

Explanation

Wave speed equals frequency multiplied by wavelength: 50 Hz x 2.0 m = 100 m/s. Frequency is cycles per second and wavelength is meters per cycle, so their product has units of meters per second.

Question 44Life and Physical Sciences (biology, chemistry, physics)

Two atoms of the same element that contain different numbers of neutrons are called

  1. Isomers
  2. Allotropes
  3. Ions
  4. Isotopes Correct answer.

Explanation

Isotopes share the same atomic number but differ in mass number because of differing neutron counts, such as carbon-12 and carbon-14. Ions differ in electron count, isomers differ in molecular arrangement, and allotropes are different structural forms of an element.

Question 45Life and Physical Sciences (biology, chemistry, physics)

Resistors of 2 ohms, 3 ohms, and 5 ohms are connected in series. What is the total resistance of the combination?

  1. 30 ohms
  2. 10 ohms Correct answer.
  3. 3.3 ohms
  4. 1.0 ohm

Explanation

In a series circuit the same current passes through each resistor and the resistances add directly: 2 + 3 + 5 = 10 ohms. Reciprocal (parallel) rules apply only when resistors are connected across the same two nodes.

Question 46Life and Physical Sciences (biology, chemistry, physics)

A woman who carries an X-linked recessive allele for red-green color blindness has children with a man who has normal color vision. What fraction of their children are expected to be colorblind sons?

  1. 1/2
  2. 1/4 Correct answer.
  3. 0
  4. 1/8

Explanation

Sons receive a Y chromosome from the father, so each son has a 1/2 chance of inheriting the mother's affected X. Because only half of all children are sons, the overall probability is 1/2 x 1/2 = 1/4.

Question 47Life and Physical Sciences (biology, chemistry, physics)

In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is 0.2. What is the expected frequency of heterozygous individuals?

  1. 0.04
  2. 0.32 Correct answer.
  3. 0.16
  4. 0.64

Explanation

With q = 0.2, the dominant allele frequency p = 0.8, and heterozygote frequency is 2pq = 2(0.8)(0.2) = 0.32. The homozygote frequencies are p squared and q squared, not the heterozygote term.

Question 48Life and Physical Sciences (biology, chemistry, physics)

A reaction has a theoretical yield of 20.0 g of product, but only 15.0 g is actually collected. What is the percent yield?

  1. 5.0%
  2. 133%
  3. 33%
  4. 75% Correct answer.

Explanation

Percent yield is the actual yield divided by the theoretical yield, multiplied by 100: (15.0 g / 20.0 g) x 100 = 75%. Actual yield cannot exceed what stoichiometry allows in a simple calculation.

Question 49Life and Physical Sciences (biology, chemistry, physics)

An object is released from rest and falls 45 m to the ground. Neglecting air resistance and using g = 10 m/s², how long does the fall take?

  1. 4.5 s
  2. 9.0 s
  3. 2.1 s
  4. 3.0 s Correct answer.

Explanation

For free fall from rest, distance equals one-half g times time squared. Solving 45 = 5t² gives t² = 9, so t = 3.0 s.

Question 50Life and Physical Sciences (biology, chemistry, physics)

A radioactive sample has a half-life of 5 days and initially contains 80 g of the isotope. How much of that isotope remains after 15 days?

  1. 5 g
  2. 20 g
  3. 10 g Correct answer.
  4. 26.7 g

Explanation

Fifteen days equals three half-lives, so the amount is halved three times: 80 g to 40 g to 20 g to 10 g. Dividing the initial mass by the number of half-lives instead of by two per half-life gives an incorrect result.