For labeling problems, use the simple formula:
\[
\boxed{
\text{Number of Labelled Nucleotides}
=
\frac{\text{Percentage Efficiency}}{100}
\times
\text{Total Nucleotides}
}
\]
For this question,
\[
10\%\ \text{of}\ 1000
=
100
\]
This type of direct percentage calculation is commonly asked in biotechnology entrance examinations.