Acetals are

Identify the reaction in which the carbonyl group of aldehydes and ketones is reduced to a methylene group upon treatment with hydrazine followed by heating with sodium hydroxide in ethylene glycol.

Acetaldehyde forms a white crystalline precipitate on mixing with a ...... solution of

$CH_3-CH=CH-CH_2OH \xrightarrow{PCC} CH_3-CH=CH-CHO$
What is the change in hybridisation at $C-1$ in the above reaction?

Identify the product of the following reaction:
$CH_3-CO-CH_2-CH_2-CH_2-CHO \xrightarrow{NaOH, \Delta} \text{Product}$

Fehling solution reacts with $HCHO$ to form a precipitate of which color?