Question

which molecular formula does not represent an unsaturated hydrocarbon?
c₆h₁₂
c₄h₆
c₇h₁₂
c₅h₁₀
c₈h₁₈
question 11 (10 points)
the molecules cis-2-pentene and trans-2-pentene are an example of a pair of ______.
isotopes
stereoisomers
constitutional isomers
identical molecules
unrelated molecules

Explanation:

First Question (Which molecular formula...):

Step1: Recall hydrocarbon types

Saturated hydrocarbons (alkanes) have formula $C_nH_{2n + 2}$. Unsaturated have double/triple bonds (alkenes: $C_nH_{2n}$, alkynes: $C_nH_{2n - 2}$).

Step2: Analyze each formula

• $C_6H_{12}$: $n = 6$, $2n = 12$ → alkene (unsaturated).
• $C_4H_6$: $n = 4$, $2n - 2 = 6$ → alkyne (unsaturated).
• $C_7H_{12}$: $n = 7$, $2n - 2 = 12$ → alkyne (unsaturated).
• $C_5H_{10}$: $n = 5$, $2n = 10$ → alkene (unsaturated).
• $C_8H_{18}$: $n = 8$, $2n + 2 = 18$ → alkane (saturated, not unsaturated).

• Isotopes: Same element, different neutrons (not molecules).
• Stereoisomers: Same formula/connectivity, different 3D arrangement (cis - trans are geometric stereoisomers).
• Constitutional isomers: Different connectivity (cis - trans have same connectivity).
• Identical molecules: cis - trans differ in structure.
• Unrelated molecules: They are related (same formula, different structure).

Answer:

$C_8H_{18}$

Second Question (cis - 2 - pentene and trans - 2 - pentene...):