Density Practice Questions
18 free Density practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following formulas correctly expresses the physical definition of density?
- A $\text{Density} = \text{Mass} \times \text{Volume}$
- B $\text{Density} = \text{Volume} / \text{Mass}$
- C $\text{Density} = \text{Mass} / \text{Volume}$
- D $\text{Density} = \text{Force} / \text{Area}$
Correct answer: $\text{Density} = \text{Mass} / \text{Volume}$
Density is fundamentally defined as the mass of a substance per unit volume ($\rho = m / V$). Its standard SI unit is kilograms per cubic meter ($\text{kg/m}^3$), though grams per cubic centimeter ($\text{g/cm}^3$) is also widely used in laboratory settings.
What is the standard density of pure liquid water at its temperature of maximum density ($4^\circ\text{C}$)?
- A $0.5\text{ g/cm}^3$
- B $1.0\text{ g/cm}^3$
- C $10.0\text{ g/cm}^3$
- D $13.6\text{ g/cm}^3$
Correct answer: $1.0\text{ g/cm}^3$
Pure liquid water reaches its maximum density of exactly $1.0\text{ g/cm}^3$ (or $1000\text{ kg/m}^3$) at $4^\circ\text{C}$. This standard value serves as the universal baseline for determining the specific gravity of all other liquid and solid materials.
A golden crown has a mass of 965 grams and a total volume of 50 cubic centimeters. What is the calculated density of the crown?
- A $4.83\text{ g/cm}^3$
- B $19.3\text{ g/cm}^3$
- C $48.25\text{ g/cm}^3$
- D $915.0\text{ g/cm}^3$
Correct answer: $19.3\text{ g/cm}^3$
Using the density equation $\rho = m / V$, we divide the mass of 965 grams by the volume of 50 cubic centimeters. This calculation yields $965 / 50 = 19.3\text{ g/cm}^3$, which corresponds exactly to the known density of pure 24-karat gold.
Why does a solid ice cube float on top of a glass of liquid water, whereas a solid piece of iron sinks instantly?
- A Ice has a higher density than liquid water simply because it is much colder than the surrounding water.
- B Ice's open crystalline structure makes it less dense than water; iron is denser.
- C The liquid water exerts zero buoyant force on the iron piece.
- D Iron has a lower mass than an equivalent volume of ice.
Correct answer: Ice's open crystalline structure makes it less dense than water; iron is denser.
According to the principle of flotation, an object will float if its density is less than that of the surrounding fluid. As water freezes, its molecules organize into an open hexagonal lattice that occupies more volume, making ice less dense than liquid water. Iron atoms are tightly packed and heavy, resulting in a density far greater than water, causing it to sink.
An object has a specific gravity of 0.75. If placed into a large basin of pure water, how will this object behave?
- A It will sink rapidly to the very bottom.
- B It will float with $75\%$ of its volume submerged beneath the water surface.
- C It will dissolve completely within a few seconds.
- D It will hover perfectly balanced in the center of the liquid column without ever moving at all.
Correct answer: It will float with $75\%$ of its volume submerged beneath the water surface.
Specific gravity is the ratio of a material's density to the density of water. A specific gravity of 0.75 means the object is exactly $75\%$ as dense as water, causing it to float with $75\%$ of its volume submerged to displace a mass of water equal to its own total mass.
What happens to the density of a standard sample of air inside a flexible balloon when it is heated, assuming the balloon expands at constant pressure?
- A The density increases because the air molecules gain mass.
- B The density decreases because the mass remains constant while the volume increases.
- C The density stays completely uniform because gas particles ignore temperature shifts.
- D The density drops instantly to absolute zero.
Correct answer: The density decreases because the mass remains constant while the volume increases.
Heating the air increases the kinetic energy of the gas molecules, forcing the flexible balloon to expand and increase its volume. Since no gas enters or leaves, the mass stays identical while the volume expands, leading to a decrease in the calculated density ($\rho = m / V$).
Which of the following instruments is specifically engineered to measure the density or specific gravity of a liquid sample directly?
- A Barometer
- B Hydrometer
- C Anemometer
- D Psychrometer
Correct answer: Hydrometer
A hydrometer is a weighted, calibrated glass tube that floats upright in a liquid. It sinks deeper in low-density liquids and rides higher in high-density liquids, allowing technicians to read the specific gravity directly from a scale on the stem.
If you mix equal volumes of three immiscible liquids—honey ($\rho = 1.42\text{ g/cm}^3$), water ($\rho = 1.00\text{ g/cm}^3$), and olive oil ($\rho = 0.92\text{ g/cm}^3$)—in a glass cylinder, how will they arrange themselves from top to bottom?
- A Honey at the top, water in the middle, olive oil at the bottom
- B Water at the top, olive oil in the middle, honey at the bottom
- C The liquids will mix perfectly to form a single uniform layer
- D Olive oil at the top, water in the middle, honey at the bottom
Correct answer: Olive oil at the top, water in the middle, honey at the bottom
Immiscible liquids stack themselves strictly in order of their densities, with the least dense fluid floating to the very top and the most dense settling at the bottom. Olive oil is the least dense and forms the top layer, water forms the middle layer, and honey is the densest, forming the bottom layer.
How does the density of a uniform iron nail compare to the density of a massive solid iron anvil?
- A The anvil has a much higher density than the nail because it is heavier.
- B The nail has a much higher density than the anvil because it is smaller.
- C They have the exact same density because density is an intrinsic property of the material.
- D The densities absolutely cannot be compared or determined without first knowing the local atmospheric pressure and altitude.
Correct answer: They have the exact same density because density is an intrinsic property of the material.
Density is an intensive or intrinsic physical property, meaning it depends solely on the chemical composition and atomic structure of the material, not the amount of matter present. Because both objects are made of solid iron, their mass-to-volume ratio remains identical.
Why does salt water have a higher density than pure fresh water at the same temperature?
- A Salt molecules chemically destroy and permanently break apart the surrounding water molecules, reducing the total volume.
- B Salt turns the water into a solid crystal lattice.
- C The dissolved salt lowers the gravitational pull on the liquid.
- D Dissolved sodium and chloride ions fit between water molecules, adding mass to a given volume.
Correct answer: Dissolved sodium and chloride ions fit between water molecules, adding mass to a given volume.
When salt dissolves in water, the sodium and chloride ions break apart and nestle into the intermolecular spaces of the water solvent without causing a massive expansion in volume. This packs more mass into the same volume of liquid, increasing the overall density of the brine.
An irregular rock sample has a mass of 60 grams. When dropped into a graduated cylinder filled with water, the water level rises from $30\text{ mL}$ to $50\text{ mL}$. What is the density of the rock?
- A $1.2\text{ g/cm}^3$
- B $2.0\text{ g/cm}^3$
- C $3.0\text{ g/cm}^3$
- D $4.0\text{ g/cm}^3$
Correct answer: $3.0\text{ g/cm}^3$
The volume of the irregular rock is found using the water displacement method: $50\text{ mL} - 30\text{ mL} = 20\text{ mL}$ (which is equivalent to $20\text{ cm}^3$). Dividing the mass of 60 grams by the volume of $20\text{ cm}^3$ yields a density of $3.0\text{ g/cm}^3$.
Which of the following physical states of matter generally exhibits the lowest density under standard temperature and pressure conditions?
- A Solid
- B Liquid
- C Gases
- D Plasma
Correct answer: Gases
In gases, the intermolecular forces are weak, allowing the molecules to spread far apart from one another. This results in vast amounts of empty space between particles, leading to a much smaller mass within a given volume compared to highly packed solids and liquids.
A liquid has a total volume of $200\text{ cm}^3$ and a mass of 160 grams. What is its density, and will it float or sink in pure water?
- A $0.8\text{ g/cm}^3$; it will float.
- B $1.25\text{ g/cm}^3$; it will sink.
- C $0.8\text{ g/cm}^3$; it will sink.
- D $1.25\text{ g/cm}^3$; it will float.
Correct answer: $0.8\text{ g/cm}^3$; it will float.
The density is calculated as $160\text{ grams} / 200\text{ cm}^3 = 0.8\text{ g/cm}^3$. Since its density is less than the density of pure water ($1.0\text{ g/cm}^3$), the liquid will float on top of the water.
When a gas sample is compressed inside a rigid steel syringe by pushing a plunger inward at constant temperature, how do its mass and density change?
- A Mass increases, and density decreases.
- B Both mass and density decrease to zero.
- C Mass decreases, and density remains constant.
- D Mass remains constant, and density increases.
Correct answer: Mass remains constant, and density increases.
Pushing the plunger reduces the volume available to the gas while keeping the total amount of gas matter (mass) identical. Since the same mass is forced into a smaller space, the density increases.
Which transition metal has the highest known standard density, making it one of the heaviest elements on Earth?
- A Aluminum
- B Iron
- C Lead
- D Osmium
Correct answer: Osmium
Osmium is the densest naturally occurring element, with an extraordinary density of approximately $22.59\text{ g/cm}^3$. This makes it slightly denser than iridium and nearly twice as dense as lead.
How does the phenomenon of thermal expansion affect the density of most solid metals when they are heated?
- A The density increases as the metal expands.
- B The density remains unchanged because solids are completely rigid.
- C The density decreases because the volume increases while mass remains constant.
- D The density fluctuates in a completely random and unpredictable manner depending on the visible color of the metal.
Correct answer: The density decreases because the volume increases while mass remains constant.
Thermal expansion causes the atoms in a metal to vibrate more vigorously and push slightly further apart, increasing the overall volume of the solid. Because the mass remains constant, this increase in volume results in a lower overall density.
A hydrometer sinks to a scale reading of 1.025 when placed in liquid A, and sinks deeper to a reading of 0.850 when placed in liquid B. What can be concluded?
- A Liquid A is less dense than liquid B.
- B Both liquids have a density perfectly identical to water.
- C Liquid A is considerably denser than liquid B.
- D Liquid B has more mass per unit volume than liquid A.
Correct answer: Liquid A is considerably denser than liquid B.
A higher hydrometer reading means the fluid is denser and exerts a stronger buoyant force, supporting the device higher up on its stem. Therefore, liquid A ($\rho = 1.025\text{ g/cm}^3$) is significantly denser than liquid B ($\rho = 0.850\text{ g/cm}^3$).
What basic configuration allows a massive steel aircraft carrier weighing over 100,000 tons to float safely on ocean water?
- A Its hollow hull traps air, reducing average density below that of water.
- B It is painted with a special hydrophobic chemical compound.
- C The engines constantly pump water upward to keep it suspended.
- D The steel undergoes a complete structural phase change instantly when exposed to ordinary salt water and pressure.
Correct answer: Its hollow hull traps air, reducing average density below that of water.
While steel itself is much denser than water, the ship is built with a massive hollow hull containing trapped air. The average density of the entire ship (steel, air, and cargo combined) is less than the density of water, allowing it to float according to Archimedes' Principle.