Verifying if molecular mass of X equals half that of Y

Steps:

• Calculate masses: A, X (C₂H₅Cl)=24+5+35.5=64.5, Y (C₂H₃OCl)=24+3+16+35.5=78.5; 2×64.5=129≠78.5.
• For B: X (C₃H₈)=36+8=44, Y (C₃H₇Cl)=36+7+35.5=78.5; 2×44=88≠78.5.
• For C: X (C₃H₆O)=36+6+16=58, Y (C₄H₈O)=48+8+16=72; 2×58=116≠72.
• For D: X (CO₂)=12+32=44, Y (C₄H₈O₂ ethyl acetate)=48+8+32=88; 2×44=88=88.

Why D is correct:

• Molecular mass equals sum of atomic masses; CO₂ (44) is exactly half of ethyl ethanoate (88) since 2×44=88.

Why the others are wrong:

• A: 2×64.5=129 exceeds 78.5.
• B: 2×44=88 exceeds 78.5.
• C: 2×58=116 exceeds 72.

Final answer: D