GKFix MCQ Question

In the Lens Maker's Formula, 1/f = (n2/n1 - 1)(1/R1 - 1/R2), what does 'n1' usually represent?

• A. Refractive index of the lens material
• B. Refractive index of vacuum
• C. Refractive index of the surrounding medium
• D. Numerical aperture