Correct Option
The molecular weight of hydrocarbons, particularly alkanes, increases directly with the number of carbon atoms present in their molecular structure. The general formula for alkanes is CnH2n+2. As the number of carbon atoms (n) increases, the total mass of the molecule also increases.
- Methane (CH₄): Contains one carbon atom. Its approximate molecular weight is 16 g/mol.
- Ethane (C₂H₆): Contains two carbon atoms. Its approximate molecular weight is 30 g/mol.
- Propane (C₃H₈): Contains three carbon atoms. Its approximate molecular weight is 44 g/mol.
- Butane (C₄H₁₀): Contains four carbon atoms. Its approximate molecular weight is 58 g/mol.
Therefore, the correct sequence in increasing order of molecular weights is Methane < Ethane < Propane < Butane.
Incorrect Options
Options B, C, and D present sequences that do not adhere to the increasing order of molecular weights. These options incorrectly arrange the hydrocarbons, placing molecules with higher molecular weights before those with lower molecular weights, or in a mixed, non-ascending order.