The correct answer is: None of the arguments is strong.
Argument I is not strong because it is an appeal to popularity. Just because other countries do something does not mean that it is the right thing to do.
Argument II is not strong because it is based on a false premise. There is no evidence that sex education in co-educational schools is harmful.
Argument III is not strong because it is based on a prediction that is not supported by evidence. There is no evidence that sex education will eradicate misunderstanding or make the younger generation healthier.
Argument IV is not strong because it is based on an emotional appeal. It is not clear how sex education would destroy the moral fiber or value system of a society.
In conclusion, none of the arguments presented are strong. More evidence is needed to support the claim that sex education should be taught in schools.