Q. The fluorescent dyes used in the liquid penetrant testing process are most active when energised with black light of what wavelengths? (Å stands for angstrom units)

• (A) 2.0 × 10-7m (2000Å)
• (B) 2.5 × 10-7m (2500 Å)
• (C) 3.25 × 10-7m (3250Å)
• (D) 3.65 × 10-7m (3650 Å)