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Material density is given by $ \rho =m/V$, where $m$ is mass and $V$ is volume. Again number density given by $n=N/V$, where $N$ is the total number of particle. How can I calculate number density $n$ from material density $ \rho $.

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You need to know the mass per particle $\mu$. Then number of particles = total mass / mass per particle, $N = m/\mu$. – Michael Brown Feb 18 '13 at 15:27

For atoms or molecules of a well-defined molecular mass M (in units of kg/mole), the number density can be expressed in terms of the mass density of a substance ρ (in units of kg/m3) as $$ n=\frac{N_{\rm A}}{M}\rho$$

Note that the ratio M/NA is the mass of a single atom or molecule in units of kg.

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