Yes, 'Respect the elderly.' is grammatically correct and a complete sentence. It is an imperative sentence which has an implied subject: 'You respect the elderly.'
"Not like that" can be grammatically correct, depending on the context.
Yes it is a grammatically correct
Yes! That is grammatically correct!
Yes, 'for free', is grammatically correct.
2 different meanings.1. I was touched by the respect with which they treated me.2. The respect which she showed to the elderly woman made an excellent impression on us all.
This is not grammatically correct. The correct form is 'you do not know', or the abbreviated 'you don't know'.
"That was wrong" is a grammatically correct sentence.
Yes, it is grammatically correct.
Yes, Almighty God is grammatically correct.
'Rhoda's crazy' is grammatically correct.
'What a drunkard you are' is a grammatically correct English sentence.
"For free' is grammatically correct. It is an idiom of the English language.