The correct option is A 1-Methoxybutane and 1-Methoxy-2-methyl propane
1-Methoxybutane CH3−CH2−CH2−CH2−O−CH3 and 1-Methoxy-2-methyl propane (CH3)2−CH−CH2−O−CH3 are chain isomers. They have same molecular formula and same alkyl group on either side of oxygen atom but different arrangement of the carbon chain within the alkyl group.