What distinguishes Type I diamonds?

• A. Nitrogen atoms substituting boron atoms in the lattice.
• B. Nitrogen atoms substituting carbon atoms in the lattice.
• C. Boron atoms substituting carbon atoms in the lattice.
• D. A lack of nitrogen atoms but presence of boron.

Answer: (B)

Diamonds classified as Type I are defined by nitrogen impurities in the crystal: nitrogen atoms replace carbon atoms in the diamond lattice. This substitutional nitrogen is what distinguishes Type I from Type II diamonds, which have little to no detectable nitrogen. Within Type I, nitrogen can occur as isolated atoms or in aggregates, but the key idea is that the impurity is nitrogen occupying lattice sites that would normally be carbon. The other ideas describe boron involvement or different substitution patterns that are characteristic of Type IIb diamonds (boron-related coloration) rather than Type I.