

Step 1. Identify the Reaction Components: The reaction involves the reduction of an acid chloride to an aldehyde using H2 gas in the presence of palladium on barium sulphate (Pd-BaSO4).
Step 2. Characteristics of Rosenmund Reduction: This specific reduction, where an acid chloride is reduced to an aldehyde, is known as the Rosenmund reduction. In this process, the use of Pd-BaSO4 prevents further reduction of the aldehyde to an alcohol.
Step 3. Conclude with the Recognized Reaction: Thus, the partial reduction of the acid chloride to an aldehyde in this reaction confirms it as a Rosenmund reduction.
The number of solutions of the equation $ \cos 2\theta \cos \left( \frac{\theta}{2} \right) + \cos \left( \frac{5\theta}{2} \right) = 2 \cos^3 \left( \frac{5\theta}{2} \right) $ in the interval \(\left[ -\frac{\pi}{2}, \frac{\pi}{2} \right ]\) is: