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

• A
  $2.5 \times 10^{30} \text{ atoms}/cm^3$
• B
  $1.0 \times 10^{13} \text{ atoms}/cm^3$
• C
  $1.0 \times 10^{15} \text{ atoms}/cm^3$
• D
  $2.5 \times 10^{36} \text{ atoms}/cm^3$