The term “Reasonable”, works as an umbrella term which could include both most prudent and even far sighted actions to exempt you from criminal liability. But for an action to be considered reasonable, it depends on the circumstances. If an intruder breaks into your house and causes sufficient apprehension of hurt to your person or property, you’re under full legal right to defend yourself according to sec 34 of BNS, Right of Private Defence, but the force used should be reasonable and necessary,
1. The act must be under reasonable apprehension of hurt/harm.
2. The harm/hurt should be subsisting. If the intruder has left or escaping and you keep on using unnecessary force, won't count as a reasonable.
3. The force is to be proportional to the act of the wrongdoer, if such an intruder is carrying a gun causing significant apprehension of danger to life, a force of similar decree can be used whereas if he is unarmed, using any force as in knife or gun may not be reasonable.
4. Will any other prudent person take a similar action if put in your shoes.
Reasonability of any action significantly depends on the circumstances under which such action is taken.