Final answer:
The numerical aperture (NA) of an oil immersion lens is typically around 1.25 to 1.40. Since no exact value is given and the refractive index for oil immersion is high, the closest provided choice to the approximate NA is 1.0.
Step-by-step explanation:
The numerical aperture (NA) of a microscope objective lens quantifies its ability to gather light and to resolve fine details of a specimen. In an oil immersion lens, the immersion medium placed between the objective lens and the immersion cover glass has a high refractive index, typically around 1.51, which is quite close to the refractive index of the glass. This serves to minimize the mismatch in refractive indices when light transitions between the cover slip and the lens, allowing for a higher numerical aperture.
The formula to calculate NA is NA = n sin α, where n is the refractive index of the medium and α is the acceptance angle of the lens. Considering the information given, we know that the refractive index for oil immersion is roughly 1.51. When combined with the ability of oil immersion lenses to have acceptance angles large enough to achieve NA values greater than 1.0, we conclude that the numerical aperture in an oil immersion lens is typically approximately 1.25 to 1.40, which means that the closest answer choice provided would be 1.0.