Of a normal couple, half the sons are haemophilic while

Of a normal couple, half the sons are haemophilic while half the daughters are carriers. The gene is located on

1. X-chromosome of father
2. Y-chromosome of father
3. one X-chromosome of mother
4. both the X-chromosomes of mother

Since half the sons are haemophilic so the genes for haemophilia is located on X-chromosome of mother.