In pure semiconductor number of conducting electrons is $5 \times 10^{20}$ per cubic meter. How many holes are there in $1 cm^3$ of the same semiconductor.

Question

$(a)\;5 \times 10^{14} \\ (b)\;5 \times 10^{-14} \\ (c)\;10^{-10} \\ (d)\;5 \times 10^{20}$