It depends on what you're asking it for. If you say, "I'm up for the challenge," then yes, it is.
The phrase "up for the challenge" is idiomatic English; it is perfectly understandable and acceptable for informal purposes. However if you are writing formally, then I would not recommend it.
"That was wrong" is a grammatically correct sentence.
Yes, Almighty God is grammatically correct.
Yes, it is grammatically correct.
This sentence is grammatically correct.
This sentence is not grammatically correct. For the sentence to be grammatically correct, the space between "in" and "to" would have to be removed. Therefore the sentence should read "They are into skating."
"Not like that" can be grammatically correct, depending on the context.
Yes! That is grammatically correct!
Yes, 'for free', is grammatically correct.
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.
'What a drunkard you are' is a grammatically correct English sentence.
Yes, Almighty God is grammatically correct.
Yes, it is grammatically correct.
Sure. It would also be grammatically correct to write He spoggled his nubbix on the goober. Grammatically correct and meaningful are not the same.
The phrase "Is you don't miss me do you" is not grammatically correct. It should be rephrased to something like "Don't you miss me?" to be correct.
No, it is not grammatically correct. The correct way to say it is "your older sister."
Saying, "I am annoyed of the way you behave.", is grammatically correct.