Match List - I with List - II. List - I List - II Pair of Compounds...

Analyzing the pairs of compounds in List-I:

A. 2-Methylpropene ($CH_3-C(CH_3)=CH_2$) and but-1-ene ($CH_3-CH_2-CH=CH_2$) have the same molecular formula $C_4H_8$ but different carbon skeletons (branched vs straight chain). Thus, they are chain isomers. (A-III)

B. Cis-but-2-ene and trans-but-2-ene are geometrical isomers, which fall under the category of stereoisomers. (B-I)

C. 2-Butanol ($C_4H_9OH$) and diethyl ether ($C_2H_5-O-C_2H_5$) have the same molecular formula $C_4H_{10}O$ but different functional groups (alcohol vs ether). Thus, they are functional group isomers. (C-IV)

D. But-1-ene and but-2-ene have the same carbon chain and functional group but differ in the position of the double bond (at $C_1$ vs $C_2$). Thus, they are position isomers. (D-II)

Matching the pairs: A-III, B-I, C-IV, D-II.