Rectified spirit is an aqueous solution which contains about _____ of ethanol:

The general molecular formula of alkynes is _____.

(A) ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$                    (B) ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$                 (C) ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$

Enter your correct answer as A, B or C.

Classify the following compound based on the pattern of the carbon chain and give its structural formula:

Propane