Reaction products and molecular masses Steps:

• Identify reaction type: A and B are SN2 substitutions; C is SN1/SN2 substitution; D is E2 elimination due to secondary halide and ethanolic base.
• Determine major organic products: A gives CH3CH2CN; B gives CH3CH2OH; C gives (CH3)2CHOH; D gives CH3CH=CH2.
• Calculate relative molecular masses: A=55, B=46, C=60, D=42.
• Compare: D has the lowest mass.

Why D is correct:

• Concentrated ethanolic NaOH favors E2 elimination on secondary halide, yielding propene (C3H6, Mr=42) per Zaitsev's rule.

Why the others are wrong:

• A: CN- acts as nucleophile in SN2, forming propanenitrile (Mr=55).
• B: Aqueous OH- promotes SN2 hydrolysis to ethanol (Mr=46).
• C: Aqueous OH- on secondary halide gives SN1/SN2 substitution to propan-2-ol (Mr=60).

Final answer: D