Option a ‘Safe’ means to be protected against any reasonably risk or danger. The meaning has no relation with the antonym of Defensive. The antonym should mean something of aggressive nature which is hostile or combative. Such expression doesn’t come from the word ‘Safe’. So, option a is inaccurate.
Option b ‘Offensive’ means causing someone resentment or annoyance and features a sense of aggressiveness. This word exactly matches the meaning of the antonym which the given word should have. So, option b is that the correct option.
Option c ‘Escape’ means to interrupt free from a state of confinement or to be released from someone’s control. The meaning has no reference to either the given word or its antonym. So, option c is additionally incorrect.
Option d ‘Protective’ is literally the synonym of the given word ‘Defensive’. It means to own the intention to safeguard something. So, option d is additionally incorrect.

Note: The meaning of the given word should be understood properly to seek out its antonym.