Which phase begins with the condensation of chromosomes along their longitudinal axis?

In which phase of mitosis does the nucleolus disappear and the chromosomes become distinct?

$A$ stage in cell division is shown in the figure. Select the answer which gives correct identification of the stage with its characteristics.

In the given figure,what is the structure $X$ composed of?

Read the following statements:
$(a)$ Complete disintegration of the nuclear envelope marks the start of the second phase of mitosis.
$(b)$ Metaphase chromosome is made up of one sister chromatid.

Which structure is generally not observed in the dividing cells of higher plants?