Question

Given below are two statements:
Statement I: Due to increase in van der Waals forces, the order of boiling points is $CH₃CH₂CH₂I>CH₃CH₂I>CH₃I$.
Statement II:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Boiling points are primarily determined by the strength of intermolecular forces (like van der Waals forces), which increase with molecular mass and surface area. Melting points also depend on how efficiently molecules pack into a crystal lattice. 
Step 2: Key Formula or Approach: 
For Statement I, compare the surface area and molecular weight of alkyl halides. For Statement II, compare the symmetry and physical properties of dichlorobenzene isomers. 
Step 3: Detailed Explanation: 
Statement I: As the size of the alkyl group increases ($CH_3 < C_2H_5 < C_3H_7$), the surface area and molecular mass increase, leading to stronger van der Waals forces. Thus, the boiling point increases. (True) 
Statement II: The \textit{para}-isomer ($p$-dichlorobenzene) is highly symmetrical, allowing it to pack closely in the crystal lattice, resulting in a much higher melting point than the \textit{ortho} or \textit{meta} isomers. However, the boiling points of all three isomers are nearly identical ($\approx 446-448$ K); the $p$-isomer is not significantly lower than the $m$-isomer. (False) 
Step 4: Final Answer: 
Statement I is true, but Statement II is false.