Classification of Functional Groups

Q. Which of the following statement is true for aldehydes and ketones?

1. Aldehydes are considered as subsets of ketones.
2. The carbonyl group for aldehydes is always at the end of the molecule.
3. Aldehydes are formed only for carbon compounds with less than 5 carbon atoms.
4. Both exhibit similar physical properties.

Q. Which one is the formula of formaldehyde?

1. $HCHO$
2. $C{H}_{3}CHO$
3. $C{H}_{3}COOH$
4. $C{H}_{3}OH$