Answer:
The national anthem will be sung at the memorial by one of the boys in the group.
Explanation:
→ Identify the subject and the object - One of the boys in the group and the national anthem
→ interchange their places, the object comes first in the passive voice and the subject comes at the end; add by before the subject since he is the doer
→ tense of the verb remains the same, but it comes in the passive form - be + past participle of the verb ( will sing changes to well be sung)