NCERT Class 9 Science — Chapter 3: Gravitation

mcqeasy

The SI unit of density is:

Official previous-year question

Verified 1 Aug 2026.

Options

A$kg m^{-2}$
B$g cm^{-3}$
C$kg m^{-3}$
D$N m^{-3}$

Did you get this right?

Solution

The correct option is

$kg m^{-3}$

Explanation

Density is a physical quantity defined as mass per unit volume. In the International System of Units (SI), derived units are constructed from the seven base units. The calculation of the unit for density requires the base unit for mass and the derived unit for volume.

Detailed Analysis

Formula for Density: $\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}$
SI Unit of Mass: The kilogram ($kg$).
SI Unit of Volume: The cubic meter ($m^3$), derived from the base unit of length (meter).
Derivation: Substituting the units into the formula:
$\text{Unit of Density} = \frac{kg}{m^3} = kg m^{-3}$

Analysis of Incorrect Options:

$kg m^{-2}$ $kg m^{-2}$: This represents surface density (mass per unit area).
$g cm^{-3}$ $g cm^{-3}$: This is the unit of density in the CGS (Centimetre-Gram-Second) system, not the SI system.
$N m^{-3}$ $N m^{-3}$: This represents specific weight (weight per unit volume), where Newton ($N$) is the unit of force.

Key Takeaway: The SI unit of density is a derived unit obtained by dividing the base unit of mass ($kg$) by the derived unit of volume ($m^3$), resulting in $kg m^{-3}$.

Your note

More from Chapter 3: Gravitation

With reference to the concept of Pressure, consider the following statements: 1. Pressure is defined as the area acting per unit thrust. 2. For a given force, pressure increases as the area of contact decreases. 3. The SI unit of pressure is Pascal (Pa). Which of the statements given above is/are correct?

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Which one of the following statements regarding the mass of an object is NOT correct?

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According to Archimedes’ Principle, the upward buoyant force experienced by a body immersed in a fluid is equal to:

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Which of the following instruments are based on Archimedes’ Principle? 1. Lactometers 2. Hydrometers 3. Odometers 4. Barometers Select the correct answer using the code given below:

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Consider the following statements about the density of a substance: 1. It is defined as mass per unit volume. 2. If the density of an object is less than that of a liquid, it will sink in that liquid. 3. The density of a substance is a characteristic property. Which of the statements given above is/are correct?

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The correct option is

$kg m^{-3}$

Explanation

Detailed Analysis

Formula for Density: $\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}$
SI Unit of Mass: The kilogram ($kg$).
SI Unit of Volume: The cubic meter ($m^3$), derived from the base unit of length (meter).
Derivation: Substituting the units into the formula:
$\text{Unit of Density} = \frac{kg}{m^3} = kg m^{-3}$

Analysis of Incorrect Options:

$kg m^{-2}$ $kg m^{-2}$: This represents surface density (mass per unit area).
$g cm^{-3}$ $g cm^{-3}$: This is the unit of density in the CGS (Centimetre-Gram-Second) system, not the SI system.
$N m^{-3}$ $N m^{-3}$: This represents specific weight (weight per unit volume), where Newton ($N$) is the unit of force.

Key Takeaway: The SI unit of density is a derived unit obtained by dividing the base unit of mass ($kg$) by the derived unit of volume ($m^3$), resulting in $kg m^{-3}$.