According to the question
Magnification \((\mathrm{m})=\frac{1}{n}\) (image is of \(\frac{1}{n^{t h}}\) the size of object).
Focal length \(=f\) (positive for convex mirror).
Object distance \(=-u\).
Now By formula.
$$
\begin{aligned}
&\mathrm{m}=\frac{f}{f-u} \\
&\Rightarrow \frac{1}{n}=\frac{f}{f+u} \\
&\Rightarrow \mathrm{f}+\mathrm{u}=\mathrm{nf} \\
&\Rightarrow \mathrm{u}=\mathrm{nf}-\mathrm{f} \\
&\Rightarrow \mathrm{u}=(\mathrm{n}-1) \mathrm{f} .
\end{aligned}
$$
Therefore the object distance from the mirror is \((n-1) f\). Hence the option \(C\) is correct
