From the compounds given below, number of compounds which give...

In Fehling’s solution, the reaction between copper(II) ions and aliphatic aldehyde is represented as;

$RCHO + 2{Cu}^{2 +} + 5{OH}^{-} \to {RCOO}^{-} + {Cu}_{2}O + 3{H}_{2}O$

Hence ,Acetaldehyde \left({CH}_{3}CHO\right),$Methanal \left(HCHO\right)$, and cyclohexane carbaldehyde 

compounds  gives positive Fehling's test.

Hence, the answer is $3$.