Which of the following is enucleate?

$DNA$ is concentrated in:

The chromosomes as thread-like structures in the nucleus were first described by

Hammerling's experiment on $Acetabularia$ proved the role of:

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 structure of the nuclear envelope is helpful in ...... .