Which of the following is associated with the synthesis of ribosomal $RNA$ $(rRNA)$?

Which of the following are used to define the karyotype of a species?
$1$. The number of chromosomes
$2$. The chromosome length
$3$. The positions of the centromeres

The study of nuclear cytology is called:

Ribosomal $RNA$ is synthesised in

What is the approximate diameter of a typical nucleus?

Where is the satellite found?