Hydrogen Bonding

Step 1: Understanding the Concept:
Hydrogen bonding occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (F, O, N) and is also attracted to an unshared pair on another electronegative atom.

Step 2: Detailed Explanation:
• HCl: H is bonded to Cl, but Cl is less electronegative and its size is large, making hydrogen bonding very weak in HCl. It does not form strong intermolecular H-bonds. • C H : H is bonded to C, not sufficiently electronegative. • RCH CHO: H is bonded to C, not to O or N. The H in the aldehyde group is not directly bonded to O. • RCH NHCH : Contains a -NH- group where H is directly bonded to N. N is highly electronegative, allowing for strong hydrogen bonding between molecules.

Step 3: Final Answer:
RCH NHCH shows hydrogen bonding, which corresponds to option (D).

Concept: A substance floats on another if its density is lower.

Step 1: Density comparison Hence, ice floats.

Step 2: Reason for lower density Ice has an open hexagonal crystal structure due to hydrogen bonding:
• Molecules are arranged with empty spaces (cavities)
• Volume increases
• Density decreases

Step 3: Conclusion
• Statement (A) is correct (fact)
• Statement (B) explains the reason Final Answer: C

Concept: Hydrogen bonding in water Water molecules form strong intermolecular hydrogen bonds:

Step 1: Structure of ice In ice, each water molecule forms 4 hydrogen bonds, creating a rigid open hexagonal structure. This structure has:
• Large empty spaces (cavities)
• Molecules held farther apart

Step 2: Structure of liquid water In liquid water:
• Hydrogen bonds are partially broken
• Molecules come closer together
• Structure becomes more compact

Step 3: Effect on density Ice has:
• Same mass
• Larger volume Final Answer: