Explanation:

- Honour killing refers to the act of killing a family member, often for marrying or having a relationship outside of the family or community’s expectations.

- Option 1: Domestic violence – While related to family abuse, honour killing is a specific act of killing for perceived loss of "honour", not all domestic violence cases are honour killings.

- Option 2: Physical assault – Honour killings can involve assault, but simply assaulting someone is not the same as an honour killing.

- Option 3: Condemning couples for marrying outside their caste and making them embrace death – This is the correct answer. Honour killings commonly occur when couples marry outside caste or community norms, leading to threats or acts of death.

- Option 4: Prevalent in north-eastern Indian states – Honour killings are more frequently reported in northern and north-western India, not specifically the north-east.