There is no fundamental right of a person arrested not to be detained in custody without being informed, as soon as may be, of the grounds for such arrest or for period beyond that of twenty-four hours of such arrest (excluding the time necessary for journey from place of arrest to court) without the authority of a Magistrate

Answer: Option B

According to the Constitution of India, there are certain provisions regarding the fundamental rights of persons arrested or detained:

Option A: In case of one who for the time being is an enemy alien
In the case of a person who is considered an enemy alien, there may not be a fundamental right to be informed of the grounds for arrest or to be detained beyond twenty-four hours without the authority of a Magistrate. This is due to the exceptional circumstances surrounding individuals classified as enemy aliens.

Option B: In case of one who is arrested or detained under any law providing for preventive detention
Similarly, in cases where a person is arrested or detained under any law providing for preventive detention, there may not be an inherent fundamental right to be informed of the grounds for arrest or to be detained beyond twenty-four hours without the authority of a Magistrate. Preventive detention laws often involve different procedures and considerations due to the nature of the perceived threat or risk.

Therefore, the correct answer is Option C: Both A and B.