Which lens is used to correct the defect of hypermetropia (farsightedness)?

For which of the following cases is total internal reflection of light possible?

$(a)$ What is dispersion of white light? What is the cause of such dispersion? Draw a diagram to show the dispersion of white light by a glass prism.
$(b)$ $A$ glass prism is able to produce a spectrum when white light passes through it,but a glass slab does not produce any spectrum. Explain why this is so.

When white light is incident on an object and it absorbs all the component colors and reflects none of them,what color does the object appear to be?

$A$ bifocal lens consists of both concave and convex lenses. Bifocal lenses are required by a person suffering from $.............$.
$P$ - Myopia (nearsightedness)
$Q$ - Hypermetropia (farsightedness)
$R$ - Presbyopia

What happens to the lens and the ciliary muscles when you are looking at distant objects?