Which of the following pairs of hydrocarbons are constitutional isomers of each other?

• A. $C_2{H}_6$ (ethane) and $C_3{H}_8$ (propane)
• B. $C_4{H}_{10}$ (butane) and $C_4{H}_{10}$ (2-methylpropane)
• C. $C_3{H}_8$ (propane) and $C_4{H}_{10}$ (butane)
• D. $C_5{H}_{12}$ (pentane) and $C_5{H}_{10}$ (cyclopentene)

Answer: (B)

Verified step by step guidance

1. Understand that constitutional isomers are compounds with the same molecular formula but different connectivity of atoms.
2. Compare the molecular formulas of each pair to see if they match exactly, since constitutional isomers must have identical molecular formulas.
3. For the pair C2H6 (ethane) and C3H8 (propane), note that the formulas differ, so they cannot be constitutional isomers.
4. For the pair C4H10 (butane) and C4H10 (2-methylpropane), observe that both have the same molecular formula but different structures, indicating they are constitutional isomers.
5. For the other pairs, check if the molecular formulas are the same; if not, they cannot be constitutional isomers.