Which structure is present within a chromosome?

Read the following statements $:-$
$(i)$ Centromere is present in the middle of the chromosomes and forms two equal arms.
$(ii)$ Chromosome has a terminal centromere.
$(iii)$ Centromere lies close to the end of the chromosome forming one extremely short and one very long arm.
$(iv)$ Centromere lies slightly away from the middle of the chromosome resulting in one shorter arm and one longer arm.
Select the correct option as per the codes given below $:-$

The pars granulosa of the nucleolus is primarily composed of:

$DNA$ is mainly found in

Diagrammatic representation of the karyotype of a species is called:

The role of the nucleus in regulating the morphology of a plant was discovered in: