Answer:a. A cataract is a clouding of the lens. Some cataracts are congenital, but most are due to age-related hardening and thickening of the lens, diabetes mellitus, or exposure to UV rays over time. The lens can be removed and replaced
with an artificial lens.
Explanation:
<span>Valence is defined as number of electrons that are present in the outermost orbital. Oxygen is in the 16th column of the periodic table and the total number of valance electrons is determined by units place digit of the column position which is 6 for oxygen. The outermost orbital is the high energy level and there are two in that orbit. So the valance is +2.</span>
<span>Infection is the term used to describe the process through microorganisms that cause diseases. The invasion of a host by a pathogenic microorganism multiplies in the tissues and the reaction of the host to its presence and to its possible toxins and can be caused by bacteria, fungi, viruses, protozoa or prions.</span>
