Which of the following is not a straight chain hydrocarbon?

What happens when (Give equations also):
$(i)$ Methane reacts with excess of chlorine in the presence of diffused sunlight.
$(ii)$ Ethanol undergoes combustion.
$(iii)$ Ethyl alcohol reacts with acidified potassium dichromate.

What is the common name of ethanal?

$A$ carboxylic acid (molecular formula $C_{2}H_{4}O_{2}$) reacts with an alcohol in the presence of an acid catalyst to form a compound $'X'$. The alcohol on oxidation with alkaline $KMnO_{4}$ followed by acidification gives the same carboxylic acid $C_{2}H_{4}O_{2}$. Write the name and structure of $(i)$ carboxylic acid,$(ii)$ alcohol,and $(iii)$ the compound $'X'$.

$(a)$ Soaps cannot be used with hard water. Why?
$(b)$ Give the chemical composition of detergents.
$(c)$ Give one advantage of detergents over soaps.

$(a)$ Differentiate between soap and detergent.
$(b)$ Explain why soaps form scum with hard water,whereas detergents do not.