The reaction of 1,2-diols (vicinal diols) with periodic acid ($HIO_4$) is known as Malaprade oxidation. It involves the oxidative cleavage of the carbon-carbon bond between the two hydroxyl groups.

1. Mechanism: The reaction proceeds through a cyclic periodate ester intermediate.
2. Product Prediction: The bond between the carbons bearing the -OH groups breaks. Each -OH group is converted into a carbonyl group ($C=O$). A primary alcohol group ($-CH_2OH$) becomes Formaldehyde ($HCHO$). A secondary alcohol group ($-CHROH$) becomes an Aldehyde ($RCHO$).

• A tertiary alcohol group ($-CR_2OH$) becomes a Ketone ($R_2CO$).

3. Application: Ethylene glycol has the structure $HO-CH_2-CH_2-OH$. Both carbon atoms are part of primary alcohol groups. Therefore, the cleavage yields two molecules of Formaldehyde ($2HCHO$). Reaction: $CH_2OH-CH_2OH + HIO_4 \rightarrow 2HCHO + HIO_3 + H_2O$.