A spherometer is an instrument used primarily to measure the curvature of spherical surfaces (both concave and convex) and the thickness of thin plates. It cannot measure properties of liquids, such as specific rotation, which is a measure of the optical activity of a substance in solution.
So, the correct answer is option 2.
Let one focus of the hyperbola $ \frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 $ be at $ (\sqrt{10}, 0) $, and the corresponding directrix be $ x = \frac{\sqrt{10}}{2} $. If $ e $ and $ l $ are the eccentricity and the latus rectum respectively, then $ 9(e^2 + l) $ is equal to: