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

Write the structural formula of the two isomers of butane.

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

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