In human males, all the chromosomes are paired perfectly except one. This/these unpaired chromosome is/are (i) large chromosome (ii) small chromosome (iii) Y-chromosome (iv) X-chromosome

The correct option is C

(iii) and (iv)

The correct option is C.

Explanation for the correct option:

1. Humans have 23 pairs of chromosomes, out of which one pair is the sex chromosome.
2. A sex chromosome differs from other chromosomes in autosome size, form, and behaviour.
3. These sex chromosomes determine the sex of the individual.
4. Female has an identical sex chromosome which is XX, but males have a non-identical sex chromosome which is XY
5. X is normal-sized while Y is a short chromosome.
6. So in human males, sex chromosome X is not perfectly paired due to the small size of the Y chromosome.

Explanation for incorrect options:

Option A:

1. In humans, all chromosomes are paired.
2. The only difference occurs in the sex chromosome.
3. The Female has perfect pair while the male has one short Y chromosome and a regular X chromosome.

Option B:

1. The Y chromosome is seen only in males.
2. They are usually shorter in size, paired with the X chromosome which is larger than the Y chromosome.

Option D:

1. X chromosomes are seen in both males and females.
2. In females, they are paired with the same.
3. But in males, they are paired with the shorter Y chromosome.

Final answer: In human males, all the chromosomes are paired perfectly except one. These unpaired chromosomes are the X chromosome and Y chromosome.