Which of the following is not a part of a human chromosome in any phase?

ANS:A - Centriole

A centriole is an organelle (a small functional structure) inside a cell. Usually only animal cells have centrioles. Each cell has two pairs of centrioles (and each 'pair' is called a centrosome and has two centrioles arranged at right angles to each other). Centrioles are responsible for organizing something called a 'spindle' during cell division.

A centromere is a region in a chromosome. Each chromosome has two 'chromatids' joined together at the centromere (if you've seen a picture of a chromosome you'll know what I mean). And during cell division, the chromosome gets attached to the spindle at the centromere. You will learn all about it when you learn about cell division (mitosis & meiosis) at school.