Step 1: Identify the provision.
The question is about the right of private defence of the body under the Indian Penal Code, 1860. The relevant section is Section 100, which lists when this right may go as far as causing the assailant's death.
Step 2: What Section 100 covers.
Section 100 allows causing death in defence of the body only in serious situations, such as an assault that reasonably causes fear of death or grievous hurt, rape, unnatural lust, and importantly, kidnapping or abduction.
Step 3: Apply to the options.
An assault committed with the intention of kidnapping or abducting a person falls squarely within Section 100. So in that situation the defender may even cause death.
Step 4: Why trespass on vacant land is wrong.
Criminal trespass on open, vacant land relates to defence of property, not the body, and it is not the kind of grave threat that allows causing death. So option (B) is wrong.
Step 5: Why simple assault and theft are wrong.
A simple assault without a weapon does not reach the high threshold of Section 100, and theft (defence of property is under Section 103) does not let you cause death just because the value crosses a figure. So options (C) and (D) are wrong.
Step 6: Conclude.
The right extends to causing death where the assault is committed to kidnap or abduct a person.
\[ \boxed{\text{An assault committed with the specific intention of kidnapping or abducting a person}} \]