Vanillin compound obtained from vanilla beans, has total sum of oxygen atoms and $$\pi$$ electrons is __________.

The product of the following reaction is P.

The number of hydroxyl groups present in the product P is ________.

The total number of 'Sigma' and 'Pi' bonds in 2-formylhex-4-enoic acid is _________.

From the compounds given below, number of compounds which give positive Fehling's test is _________.

Benzaldehyde, Acetaldehyde, Acetone, Acetophenone, Methanal, 4nitrobenzaldehyde, cyclohexane carbaldehyde.