Rarely females experience the physiological defect of haemophilia as they do so only when they are

The correct option is "homozygous for the defect".

Haemophilia is a sex-linked recessive disorder. The gene responsible for haemophilia is located on the X chromosome.
Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY).

For a female to exhibit the symptoms of haemophilia, she must inherit the defective gene on both of her X chromosomes. This state, where an individual has two identical alleles for a particular gene, is called homozygous.
If a female has only one defective allele (heterozygous), she will be a carrier of the disorder but will not show any physiological symptoms because the normal allele on her other X chromosome is dominant and sufficient to produce the normal clotting factors.
Therefore, females rarely experience the physiological defect of haemophilia because they must be homozygous for the defect, requiring both the mother to be at least a carrier and the father to be haemophilic.