The teacher called his name ___

loud or loudly?

Both loud and loudly can be adverbs. What's the difference please?

Question

The teacher called his name ___

loud or loudly?

Both loud and loudly can be adverbs. What's the difference please?

Answer

The correct answer would be 'loudly'

If you use 'loud' in this sentence, it would serve as an adjective rather than an adverb.
Remember, loud is only used as an adverb when in phrases, or in informal language. 
Like, "The teacher called his name out loud"

Answer

Both would be appropriate, in this context you would want to use loudly due the story being told in past tense.