Yes — the sentence is grammatically correct.
Here is a simple explanation:
- "Youll" is a contraction of "you will." It is fine to use in this sentence.
- "Its" (no apostrophe) shows that something belongs to "it" (the nose belongs to the animal). Do NOT write "its" here — that means "it is."
- The phrase "In the snow," is an introductory phrase. The comma after it is okay but not always required. It makes the sentence clear.
- The ending period is correct because the sentence is a statement.
Simple alternative ways to say the same idea:
- "Only its black nose shows in the snow."
- "You will see only its black nose in the snow."
Little tip: remember its for belonging (its tail), and its for "it is" (its cold).