Why would scientists stop a cell in metaphase?

Answer 1

Metaphase is the cell division phase during which all the chromosomes are alligned at the equator ready to separate in the subsequent Anaphase.

Arresting cells in metaphase offers scientists the opportunity to look at the chromosomes and if there are any defects (in their lengths) present.

Alternatively, arresting cells in metaphase can also be used to ensures that the spindle fibers are attached to the centromeres of the chromosomes to allow for correct separation. Improper division of sister chromatids in meiosis generates various genetic disorders, more prominently when these concern X and Y chromosomes that didn't divide correctly.

Answer 2

if it is one of those premade slides, then it is most definitely dead.
Not only is it dead, it has been "fixed". Chemicals are added to the specimen before the slide is created to pretty much suspend or "freeze" everything where it was when it was processed, which is done a soon as possible after harvesting. If the fixative were not added, all of the structures would break down. Formalin is one of the more common fixatives, which is made with formaldehyde and some other things to make the formaldehyde less volatile. Embalming fluid uses formalin, some kind of alcohol, and one or two other chemicals, though it has been a few months since I've seen it, so I can't recall off the top of my head. It does basically the same thing - keeps all the parts of the cells suspended so everything keeps looking the same despite the person being dead, and also makes it much harder for bacteria to decompose whatever has been fixed. Formaldehyde used to be used on its own, but it is volatile and carcinogenic - two things that are really bad for whoever is doing the fixing.

Not only are the cells dead and fixed, they've also been stained with chemicals that make certain parts appear certain colors, as most structures in both plants and animals are relatively colorless. For the most part, the hemoglobin in our red blood cells and the melanin in our skin, eyes, and hair give us the vast majority of color that we see on the outside of our bodies, and the breakdown products of the hemoglobin are actually what give bile, feces, and urine those respective colors. The pigment in plants come from the structures that help the plant make glucose, and a few other pigmented molecules on other parts (like the flower). Different stains bind to different parts of the cell because of their chemical composition. A combination of different stains gives the product you see under the microscope - the onion where different parts are different colors.

So that long answer is to say that yes, the cells are dead.