Which of the following statements regarding carbohydrates is not correct?

Carbohydrates may be defined as polyhydroxy acetals or ketals which on hydrolysis produce hydroxy carbonyl compounds

Monosaccharides possess free carbonyl groups

The general formula of most of the carbohydrates can be written as ${\mathrm{C}}_n{\mathrm{H}}_{2n}{\mathrm{O}}_n$

The main functions of carbohydrates is to support the structure of plants and to store chemical energy as sugars and starch