1. Identify the complex in Fehling's reagent

   Fehling's reagent contains a deep blue complex of $\text{Cu}^{2+}$ with tartrate ions in alkaline medium.

   So, the metal ion responsible for magnetism is: $\text{Cu}^{2+}$

2. Find the electronic configuration of $\text{Cu}^{2+}$

   Atomic number of Cu = 29.

   Neutral copper: $\text{Cu}: [Ar] \, 3d^{10}4s^1$

   For $\text{Cu}^{2+}$, remove two electrons:

   • one from $4s$
   • one from $3d$

   Therefore, $\text{Cu}^{2+}: [Ar] \, 3d^9$

3. Count unpaired electrons

   In $3d^9$, there is: $n = 1 \text{ unpaired electron}$

4. Use spin-only magnetic moment formula

   $\mu = \sqrt{n(n+2)} \text{ B.M.}$

   Substituting $n=1$: $\mu = \sqrt{1(1+2)} = \sqrt{3} \approx 1.73 \text{ B.M.}$

5. Nearest integer

   $1.73 \approx 2$

Therefore, the spin-only magnetic moment of the complex present in Fehling's reagent is 2 B.M. (nearest integer).