Colchicine arrests spindle at

$A$ student was asked to identify a permanent slide of mitosis. He made the following observations:
$(i)$ Splitting of centromere and formation of daughter chromatids.
(ii) Chromatids are migrating towards the opposite poles.
The stage would be

In which phase are chromosomes most easily observed?

If a diploid cell is treated with colchicine,then it becomes

During cell growth,where does $DNA$ synthesis occur?

$A$ student observed a slide of mitosis under the microscope and noted that the chromosomes were positioned at the opposite poles. Which stage was the student observing?