Give one word or a phrase for: The tendency of an element to form chains of identical atoms.

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

Write the structural formula of the two isomers of butane.

Name the gas that is produced during reaction of ethanol and sodium.