Concept:Subh prayer is another name for the Fajr prayer, which is the dawn obligatory prayer in Islam.Explanation:The five daily obligatory prayers have fixed numbers of units called rak'ahs.Fajr (Subh) has 2 rak'ahs.Zuhr has 4 rak'ahs.Asr has 4 rak'ahs.Maghrib has 3 rak'ahs.Isha has 4 rak'ahs.Therefore, the obligatory rak'ahs in Subh prayer are 2.Answer:B. 2