Answer
The element's atomic mass number is 24 amu.
Work Step by Step
We can find the mass of one atom as:
$m_a = \frac{\rho}{\rho_N}$
$m_a = \frac{1750~kg/m^3}{4.39\times 10^{28}~atoms/m^3}$
$m_a = 3.986\times 10^{-26}~kg$
We can find the total number of protons or neutrons in the atom as:
$A = \frac{m_a}{1.66\times 10^{-27}~kg}$
$A = \frac{3.986\times 10^{-26}~kg}{1.66\times 10^{-27}~kg}$
$A = 24~amu$
The element's atomic mass number is 24 amu.
