Answer:
β-hydroxyaldehyde (an aldol) namely 3-Hydroxy butanal.
Explanation:
When acetaldehyde is treated with dil.NaOH it undergoes self condensation as it contains alpha-hydrogen atom in its compound forming β-hydroxyaldehyde (an aldol) namely 3-Hydroxy butanal. This compound upon further heating will eliminate a molecule of water forming aldol condensation product namely Crotonaldehyde Or But-2-en-al. see the diagram attached.
RADIATION. Radio waves, microwaves, IR, light, UV, x-rays, GAMMA waves etc are ALL Electromagnetic radiation. The difference between ALL the above is the frequency, I.E. The number of waves per second. The higher the frequency the more energy.