What is the $IUPAC$ name of formic acid?

Which of the following is a homopolymer?

Identify the unsaturated compounds from the following:
$(i)$ Propane
$(ii)$ Propene
$(iii)$ Propyne
$(iv)$ Chloropropane

Give names of the following:
$(a)$ An alcohol containing $4$ carbon atoms.
$(b)$ An acid with $5$ carbon atoms.
$(c)$ Simplest ketone. Define functional group in a carbon compound. Mention names of any three functional groups with their formulae and example.

Which of the following are correct structural isomers of butane $(C_4H_{10})$?
$(i)$ $n$-butane: $CH_3-CH_2-CH_2-CH_3$
(ii) Isobutane ($2$-methylpropane): $CH_3-CH(CH_3)-CH_3$
(iii) Cyclobutane: $A$ four-carbon ring structure $(C_4H_8)$
(iv) Ethane dimer: Not a valid isomer of butane.

What is a functional group? Give examples of four different functional groups.