Why do the chromosomes become short and thick in prophase?

Give the biological/technical terms for the following: The stage of cell division in which the nuclear membrane disappears and the chromosomes become short and thick.

The chromosomes become invisible in

The chromosomes become invisible in

In prophase, chromosomes shorten and thicken due to

In prophase, chromosomes shorten and thicken due to

In prophase, chromosomes shorten and thicken due to

In prophase, chromosomes shorten and thicken due to

Write short notes on prophase I

Write a short note on prophase.