Question

What is the ratio of hydrogen atoms present in hept-2-yne to that in but-2-ene?

• A. 3:2
• B. 3:4
• C. 5:2
• D. 6:5

Answer 1

The correct option is A 3:2

General formula for alkynes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n-2}}$.

For hept-2-yne:
$\bullet$ Word root hept represents it contains seven carbon atoms.
$\bullet$ Substituting n=7 in the general formula, no. of hydrogen atoms = $(2\times 7)-2=14-2=12$.

General formula for alkenes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}$.

For but-2-ene:
$\bullet$ Word root but represents four carbon atoms,
$\bullet$ Substituting n=4 in the general formula, the number of hydrogen atoms = $2\times 4=8$.

Thus, the ratio of number of hydrogen atoms in hept-2-yne to that in but-2-ene is 12:8, which on simplifying becomes 3:2.