What are the elements of a nebula consist of

If steel is more dense that lake water, why can a boat float

Determine the age of a fossil if it had only one eighth of its original carbon-14 content remaining?

In a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. what should be the radius of curvature of the cornea such that the image of an object 40.0 cm from the cornea’s vertex is focused on the retina?