A silicon specimen is made into a P-type semi-conductor by doping, on an average, one Indium atom per $5×10^{7}$ silicon atoms. If the number density of atoms in the silicon specimen is $5×10^{28} atoms/m^3$, then the number of acceptor atoms in silicon will be

$1.0×10^{15} atoms/cm^3$

Number density of atoms in silicon specimen = $5×10^{28} atoms/m^3 = 5×10^{22} atom/cm^3$

Since one atom of indium is doped in $5×10^7$ Si atom. So number of indium atoms doped per cm^-3 of silicon.

$n=\frac{5×10^{22}}{5×10^{7}}=1×10^{15} atoms/cm^3$