Which human cell lacks a nucleus?

The part of the chromosome after the secondary constriction is called ......

In which type of chromosome is the centromere located at the terminal end?

Which one of the following is the site for active ribosomal $RNA$ synthesis?

Some chromosomes have non-staining secondary constrictions at a constant location. This gives the appearance of a small fragment called the ......

Identify $X$ in the given diagram of a chromosome.