Question

which molecular formula does not represent an unsaturated hydrocarbon? c₆h₁₂, c₄h₆, c₇h₁₂, c₅h₁₀, c₈h₁₈

Explanation:

Step1: Recall the formula for saturated hydrocarbons

Saturated hydrocarbons (alkanes) have the general formula $C_nH_{2n + 2}$. Unsaturated hydrocarbons (alkenes: $C_nH_{2n}$, alkynes: $C_nH_{2n-2}$, or with rings) have formulas that deviate from $C_nH_{2n + 2}$.

Step2: Check each formula

• For $C_6H_{12}$: $n = 6$, $2n=12$, so it could be an alkene (unsaturated).
• For $C_4H_6$: $n = 4$, $2n - 2=6$, so it could be an alkyne (unsaturated).
• For $C_7H_{12}$: $n = 7$, $2n - 2 = 12$, so it could be an alkyne (unsaturated).
• For $C_5H_{10}$: $n = 5$, $2n = 10$, so it could be an alkene (unsaturated).
• For $C_8H_{18}$: $n = 8$, $2n+2=18$, which matches the alkane (saturated) formula. So it is not an unsaturated hydrocarbon.

Answer:

$C_8H_{18}$ (or the option with $C_8H_{18}$)