Solid State

Step 1: Hydrogen Bonding.
- Hydrogen bonds are weaker than covalent bonds. A hydrogen bond is an attractive force between a hydrogen atom covalently bonded to a more electronegative atom (e.g., oxygen, nitrogen) and another electronegative atom.
Step 2: Covalent Bonding in CH .
- CH (methane) has covalent bonds between carbon and hydrogen atoms.
Step 3: Conductivity of Covalent Compounds.
- Covalent compounds generally do not conduct electricity unless they are in molten form or dissolved in water. However, diamond is an exception because it is a covalent network solid that does not conduct electricity.
Step 4: Graphite Properties.
- Graphite is a soft solid and a good conductor of electricity due to the mobility of electrons between layers.
Step 5: Conclusion.
Thus, the correct statements are:
- Hydrogen bond is weaker than covalent bond.
- CH has covalent bonds.
- Graphite is a soft solid and a good conductor of electricity.
Final Answer:

Step 1: Face-Centered Cubic (FCC).
- In FCC, atoms are located at the corners and centers of the faces of the unit cell.
- The effective number of atoms per unit cell is 4 (not 2).
Step 2: Body-Centered Cubic (BCC).
- In BCC, there is one atom at each corner and one at the center of the unit cell.
- The effective number of atoms per unit cell is 2, not 4.
Step 3: Simple Cubic (SC).
- In SC, there is one atom at each corner of the unit cell.
- The effective number of atoms per unit cell is 1.
Step 4: Conclusion. Thus, the correct answers are:
Final Answer:

Step 1: Understand types of solids.
- Covalent crystals: Atoms are held together by covalent bonds, resulting in a very strong structure.
- Silicon (D): Forms a covalent crystal structure (diamond-like).
- Sulphur (A): Exists as S molecules in a molecular solid, not a covalent crystal.
- Iodine (B): Exists as I molecules in a molecular solid.
- Phosphorus (C): Exists in molecular form (white phosphorus), not as a covalent crystal.
Step 2: Conclusion.
Thus, only Silicon (D) forms a covalent crystal.
Final Answer: