Which is the functional group in propanone?

What is the name of the aldehyde corresponding to methane?

$A$ hydrocarbon,$C_{2}H_{4}$,decolorizes bromine water.
$(i)$ Name the hydrocarbon.
$(ii)$ Mention the family to which it belongs.
$(iii)$ Write the chemical equation of the reaction of this hydrocarbon with hydrogen.

Which among the following are unsaturated hydrocarbons?
$(i)$ $H_3C-CH_2-CH_2-CH_3$
$(ii)$ $H_3C-C\equiv C-CH_3$
$(iii)$ $H_3C-CH(CH_3)-CH_3$
$(iv)$ $H_3C-C(CH_3)=CH_2$

Write the name and structure of an aldehyde with four carbon atoms in its molecule.

Which functional group is present in carboxylic acid?