Identify the term or substance based on the descriptions given below:

(i) Ice like crystals formed on cooling an organic acid sufficiently.

(ii) Hydrocarbon containing a triple bond used for welding purposes.

(iii) The property by virtue of which the compound has the same molecular formula but different structural formulae.

(iv) The compound formed where two alkyl groups are linked by $\overset{\underset{\text{||}}{\text{O}}}{\text{-C-}}$ group.

Give a balanced chemical equation for each of the following –

(i) Preparation of ethane from sodium propionate.

(ii) Action of alcoholic KOH on bromoethane.

Choose the correct answer from the options given:

(i) The organic compound which undergoes substitution reaction is:

A: C₂H₂
B: C₂H₄
C: C₁₀H₁₈
D: C₂H₆

(ii) The IUPAC name of dimethyl ether is:

A: Ethoxy methane
B: Methoxy methane
C: Methoxy ethane
D: Ethoxy ethane

Draw the structural formula for –

(i) 2, 3 – dimethyl butane

(ii) Diethyl ether

(iii) Propanoic acid