The probability of having a haemophilia carrier daughter by a haemoph…

The correct answer is Option (3) → 25%

Carrier mother X^hX × normal father XY gives four equally likely children: X^hX (carrier daughter), XX (normal daughter), X^hY (affected son) and XY (normal son). One of the four is a carrier daughter: 25 per cent.

Option (2) 50% — Incorrect. 50 per cent is the share among the daughters only.

Option (3) 25% — Correct. The mother is a carrier (X^hX) and the father is normal (XY). Their children are XX, XY, X^hX and X^hY in equal numbers, so the chance of a carrier daughter (X^hX) is 1 in 4 = 25 per cent.

NCERT Extract:
Mendelian Disorders – “… Haemophilia : This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia may transmit the disease to sons.”