**Formula sheet for Solid State**

Solid State is an important topic in the NEET examination, and having a formula sheet handy can be extremely helpful for quick revision and problem-solving. In this article, we will provide you with a detailed formula sheet for Solid State, covering the key concepts and equations you need to know.

**1. Bravais Lattice**
- Bravais lattice: A lattice is an imaginary framework in which the points represent the constituent particles of a crystal.
- There are 14 possible Bravais lattices in three dimensions, categorized into seven crystal systems.
- Crystal systems: Cubic, Tetragonal, Orthorhombic, Rhombohedral, Monoclinic, Triclinic, Hexagonal.

**2. Unit Cell**
- Unit cell: The smallest repeating unit of a crystal lattice.
- Types of unit cells: Primitive, Body-centered (bcc), Face-centered (fcc), and Hexagonal.

**3. Density Calculation**
- Density (ρ) = (Z × M) / (a^3 × N_A), where Z is the number of atoms in the unit cell, M is the molar mass of the substance, a is the length of the edge of the unit cell, and N_A is Avogadro's number.

**4. Imperfections in Solids**
- Point defects: Vacancies, Interstitials, Substitutional, and Frenkel defects.
- Line defects: Edge dislocations and Screw dislocations.
- Surface defects: Steps, Kinks, and Terraces.

**5. Crystal Systems and Coordination Number**
- Cubic: Coordination number (CN) = 6
- Tetragonal: CN = 4 or 8
- Orthorhombic: CN = 4, 6, or 8
- Rhombohedral: CN = 3, 4, or 6
- Monoclinic: CN = 4, 6, or 8
- Triclinic: CN = 4, 6, or 8
- Hexagonal: CN = 6

**6. Packing Efficiency**
- Packing efficiency = (Volume occupied by spheres) / (Total volume of unit cell)
- Cubic (primitive) packing efficiency = π / 6 ≈ 0.52
- Cubic (body-centered) packing efficiency = π / 3 ≈ 0.68
- Cubic (face-centered) packing efficiency = π / 2 ≈ 0.74
- Hexagonal packing efficiency = 0.74

**7. X-Ray Diffraction**
- Bragg's law: nλ = 2d sinθ, where n is the order of the diffraction, λ is the wavelength of X-rays, d is the distance between atomic planes, and θ is the angle of incidence.

**8. Electrical Conductivity**
- Conductors: High electrical conductivity due to the presence of a large number of free electrons.
- Insulators: Poor electrical conductivity due to a completely filled valence band and large energy gap.
- Semiconductors: Moderate electrical conductivity due to a partially filled valence band and a small energy gap.

These are some of the key formulas and concepts that you should include in your Solid State formula sheet for NEET preparation. Regular revision and practice using these formulas will enhance your understanding and problem