Question: Why is there no 'Bismillah' in the beginning of 'Surah Baraat'? and Why we see Bismillah in the middle of Surah Naml?
Answer: Because Surah Baraat as is apparent from the following, is for the warning of polytheists and the breaker of covenant and its aim was to warn those people who were trying to destroy the light of the belief in Oneness of Allah, moral and social reformation in the Arabian Gulf thus it was not suitable that its beginning should be with Bismillah because this sentence is the sign of mercy, peace and friendship.
As far as the mention in the middle of Surah Naml is concerned it is the beginning of the letter that Sulaiman (a.s.) had written to the Queen of Saba. And since the full text of this letter is quoted in the Qur’an, the Bismillah is also mentioned because this letter began with this sentence.