What is the compound having $(-CHO)$ functional group called?

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.

Explain the given reactions with examples:
$(a)$ Hydrogenation reaction
$(b)$ Oxidation reaction
$(c)$ Substitution reaction

Draw the structure of the simplest ketone.

Look at the figure and answer the following questions:
$(a)$ If ethanol is used instead of ethanoic acid,would you expect the same change?
$(b)$ How can a solution of lime water be prepared in the laboratory?

What are soaps chemically? How do they differ from synthetic detergents? Explain the mechanism and the cleansing action of soap.